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V^ .-U^ 




A Study of the Factors Influencing 



THE 



Improvement of the Potato 



PRESENTED TO THE 



FACULTY OF THE UNIVERSITY OF ILLINOIS 

URBANA, ILLINOIS, U. S. A. 



AS A 



Thesis for the Degree of Doctor of Philosophy 

JUNE, 1907 



BY 



EDWARD MURRAY EAST, M, S. 



PUBLISHED 

BY THE UNIVERSITY OF ILLINOIS 

AGRICULTURAL EXPERIMENT STATION 

AS BULLETIN No. 127 



UNIVERSITY OF ILLINOIS 



Agricultural Experiment Station 



BULLETIN NO. 127 



A STUDY OF THE FACTORS INFLUENCING 
THE IMPROVEMENT OF THE POTATO 



By EDWARD M. EAST 




URBANA, ILLINOIS, AUGUST, 1908 



:i<? 



Table oe Contents 

PAGES. 

Introduction • - 375 

1. The Use of Other Species 378 

2. The Original Plant 380 

Original Habitat 380 

Introduction to Cultivation 380 

Two Varieties Introduced 382 

3. The Modern Plant • • 385 

Structure and Characteristics 385 

Varieties of To-day 387 

Modern Potato Breeders 390 

4. Methods of Breeding 391 

General Basis 391 

Precautions in Comparative Tests 394 

Correlations 395 

5. The Inheritance of Characters in Tuber Selections 398 

Theory 398 

Experimental Evidence 403 

6. Plypothesis of Degeneration 410 

Analysis of the Question . 410 

Biological Evidence 413 

Experimental Evidence 414 

7. Discontinuous Variations 417 

8. Graft Hybrids 418 

9. Quality . 419 

Historical 419 

Experimental 422 

Composition of Different Parts 422 

Sampling 423 

Relations Between Total Nitrogen Content and 

Quality 423 

Relations Between Dry Matter and Quality 425 

Physical Structure and Quality 426 

Other Factors Influencing Quality 429 

10. Variations in Chemical Composition as a Basis for Im- 

provement 437 

Selections for Planting in 1902 439 

Selections for Planting' in. 1903 . 443 

11. General Statements ....,'.' 447 

Bibliography 450 



It 
The . 



A STUDY OF THE FACTORS INFLUENCING THE 
IMPROVEMENT OF THE POTATO* 

By Edward M. East. 

INTRODUCTION 

Either because it possesses no strong flavor to dull the appetite, 
or possibly on account of its antiscorbutic properties, the common 
potato Solanum tuberosum L., has overcome seemingly insurmount- 
able obstacles in its claim upon the public taste and has become a 
close rival to our cereal staff of life. The high cost of production 
and general uncertainty of the return, combined with the cost of 
transportation of a perishable, bulky product, would seem to be ad- 
verse factors which might preclude any general increase in grow- 
ing the crop. Such has not been the case, however, and the 
potato, like other crops, has increased greatly in acreage in lo- 
calities best suited to it, notably the sandy soils of the northern 
states. These soils seem to be so pre-eminently fitted for its growth 
that the crops are highl}^ profitable even after deducting the cost of 
shipping long distances. During the last ten years,* * the six states 
of Maine, New York, Pennsylvania, Michigan, Wisconsin and Iowa 
have furnished an average of one-half of the total crop of the 
United States. In other sections of the country where the growing 
of large crops is more unlikely from natural reasons, as inhospitable 
soil or climate, the cost of production has been high, and over- 
producti(5n at times (as in 1895-6) has had a very disastrous effect 
upon the price, occasioning great loss to the producer. This state 
of affairs is in a great measure due to the fact that in these sec- 
tions the acreage per grower is small, and the business is not suf- 
ficiently organized to make possible long distance shipping, which 
would partially overcome the great local fluctuation in price. 

The annual consumption of potatoes per capita in the United 
States for a period of thirty years is given by the Twelfth Census 
as three and one-half bushels, and when the amount available for 
human consumption is smaller than this, — as has bee.n the case in 
the last few years, — the price precludes their use for other purposes. 



♦Submitted to the Faculty of the Graduate School of the University of Illinois in partial 
fulfillment of the requirements for the degree of Doctor of Philosophy, March, 1907. 

**U. S. Dept. of Ag-ri. Yearbook, 190S. 

375 



376 Bulletin No. 127. • \August, 

This has left capital invested in starch mills completely unpro- 
ductive, as the limiting price within which the manufacturer can 
compete is forty cents per barrel of two and one-half bushels. There 
is no doubt but that the repeal of the tax upon alcohol for indus- 
trial purposes will furnish a channel for the utilization of all future 
excess of production over that used for human consumption, should 
the manufacturers of starch, glucose, dextrin and desiccated prod- 
uct, — who can pay a slightly higher price, — be unable to utilize it. 
At the present rate of increase of our population, however, the an- 
nual increase of production for human food alone must be from 
3,000,000 to 5,000,000 bushels; and an increase, which would be a 
factor in the production of alcohol at all comparable with that of 
Germany, would have to be many times that amount. 

The broad problems which confront the grower who has to face 
these demands, are, increased yields per acre and the development 
of varieties adapted to specific purposes. In the first instance suit- 
able soil, available plant food, and proper methods of tillage and of 
combating disease will do much ; but here as well as in the second 
case, probably the possibility for as great an advance lies in the 
province of the plant breeder. 

The matter of variety efficiency to produce tubers in large quan- 
tities may be regarded as a desired accompaniment to all strains, no 
matter what other particular characters they may possess. The spe- 
cial characters, with the possession of which new varieties should be 
originated, are (i) an increase in nutritive value, (2) an improve- 
ment in table quality, and (3) a higher starch content. Coupled 
with the possession of each of these qualities should be the very 
important character of resistance to disease. ^ 

Since the potato is one of the world's cheapest food sources, if 
there is a possibility of finally obtaining varieties, which, without 
being perfect foods, yet would furnish a more nearly proper ratio 
of protein and carbohydrates; it would be an inestimable boon to 
the world's poor, for protein is a much more expensive food con- 
stituent than starch. This problem is inseparably linked with im- 
provement in general table quality, for quality must in some man- 
ner be correlated with composition. On the other hand, varieties 
should be originated which yield a large amount of starch per acre, 
for the use of those growing for the starch, glucose or alcohol 
manufacturer. It is recognized that at the present price of produc- 
tion, maize is a much cheaper source of alcohol than potatoes ; but 
with the American taste for high starch potatoes, such potatoes 
would be used as food except in times of over production, until 



i9o8.] Improvement of the Potato. 377 

cheaper methods of production and better varieties make the potato 
a competitor with the cereals for manufacturing purposes. 

This study deals with such questions as have naturally arisen in 
trying to form a basis for practical work in potato improvement; 
and includes an examination of the literature bearing upon the pos- 
sibilities of attaining this end. The principles underlying practical 
work in potato improvement are very broad, — ^much too broad to 
be adequately discussed in a single paper, — and yet it seems impos- 
sible to separate them into narrow lines without ignoring principles 
which are essential to the work. For this reason it has been thought 
best to consider briefly such of these as are indispensable, without 
regard as to whether in every case they have been touched in the 
experimental work. No attempt has been made to discuss historical, 
agricultural or economic data, however, except in so far as such 
subjects relate to the improvement of the potato in desirable hered- 
itary qualities. A considerable amount of literature has made its 
appearance since the beginning of the experimental work in 1901 ; 
but we have endeavored to give a resume of the present status of 
knowledge of the subjects. 

The writer desires to express his obligation to the Directors of 
the Illinois and Connecticut Agricultural Experiment Stations, 
E. Davenport and E. H. Jenkins, through whom was made possible 
the use of laboratory and other facilities of these stations ; and who 
have given much helpful advice. Especial acknowledgment is made 
to Dr. C. G. Hopkins under whose direction the study was under- 
taken, and who has been a constant source of advice and encour- 
asfement. 



378 Bulletin No. 127. , [Atisust, 

I. THE USE OE OTHER SPECIES 

The plant which bears the tuber which we call the potato, and 
which name has been extended to the whole plant, has a recorded 
history of only three hundred years, it having been introduced into 
Europe about the end of the sixteenth century. Its botanical char- 
acter caused it to be called Solanum tuberosum by Gaspard Bauhin 
(86) in his Phytopinax, printed at Bale in 1596. This name was 
followed by Linnaeus when binomial nomenclature was introduced. 

There are several other members of the genus which bear tubers, 
but none has yet become of commercial importance. About twenty 
tuber-bearing kinds of Solanum have been at different times classed 
as separate species. J. G. Baker (6) has given us probably our best 
classification, after having made a thorough examination of all 
species at Kew, the British Museum, and the Lindley Herbarium, 
as well as many growing specimens. He concludes that there are 
only six distinct species: S. tuberosum Linn., S. Maglia Srhlecht., 
vS^. Cominersonii Dun., S. cardiophyllum Lind., S. Jamesii Torr. and 
S. oxycarpum Schiede. Later, (7) he places 5. Maglia as a va- 
riety of vS*. tuberosum which reduces the number of species to five. 

Solanum Commersonii Dun. has been shown by Labergerie 
(65) to be in all probabiHty the most promising of the other species, 
in its commercial possibilities. In his extended investigations, it 
showed a great tendency to produce bud variations in color which 
were permanent, and which when propagated showed great differ- 
ences in the production of tubers, immunity to disease, etc. A vio- 
let variation showed absolute immunity to late blight PJi\tophthora 
infestans (Mont.) De By., for three years, w^iile plants of S. tu- 
berosum growing near were stricken.. The yield was as high as 
100,000 K. per hectare with a composition much the same as the 
common potato. Rev. J. R. Lawrence of North Middleboro, Mas- 
sachusetts, has recently stated, however, that his plants have not 
been immune to late blight. 

S. Maglia Schlecht. of Chili, S. immitc Dun. of Peru, and S. ver- 
riicosum ^chlect. of Mexico, have all been mentioned as species and 
varieties especially worthy of being tried in the hopes of finding 
strains which by selection might become of commercial value and 
be immune to certain diseases, or with which the same end might be 
reached by hybridization with S. tuberosum. No valuable com- 
mercial strains from these sources, however, have yet been pro- 
duced. 

Stuart (92) found in 1904 that S. Commersonii and S. poly- 



igoS.] Improvement of the Potato. 379 

adcnuiin were quite resistant to late blight, while S. stolonifcrnm 
was not. In his later (93) report of 1905, they all showed a high 
percentage of infection. None of these species or varieties gave 
marketable tubers in his tests, but they had hardly been cultivated 
by him long enough to have become adapted to Vermont conditions. 
De Candolle (22 p. 49) mentions that vS'. verrucosum is not dis- 
ease resistant. 

It seems unlikely from past results, that there will be any great 
progress made through straight selections of other species, if we 
except S. Commersonii. This species has been thus far very unsat- 
isfactory in the United States, but there is in it still cause for ex- 
periment. It is very variable in its habits of growth, length of 
stolons, shape of tubers and other important characters ; hence there 
may in time be some promising strains isolated. Until we have 
such strains established, there will probably be little good from 
hybridizing mediocre elementary species with the common potato, 
for the hybridization is effected with difficulty. 

For two seasons the writer has had under observation some 
plants grown from tubers of Labergerie's stock imported by J. J. H. 
Gregory and son, Marblehead, Massachusetts. Phytophthora in- 
festans has not been troublesome during either of these seasons; 
hence, no data have been obtained regarding the comparative re- 
sistance of the plants to the fungus. I am compelled to state, how- 
ever, that in no character of leaf, stem, flower or tuber, is 
the plant different from common purple tubered varieties of S. tu- 
berosum. Either there has been some mistake in Labergerie's 
seemingly careful work, and there has been a mixture with tubers 
of S. tuberosum; or we must conclude that there have been bud 
mutations in at least five or six characters of S. Commersonii, giving 
a plant indistinguishable from vS'. tuberosum. The truth of the latter 
conclusion would give us a unique phenomenon that is of extreme 
importance to science, and the case must be confirmed before it is 
accepted as a fact. 

Our plants have flowered freely, but viable pollen has been pro- 
duced in extremely small quantities. Numerous attempts at hybrid- 
izing with S. tuberosum have all failed. 



380 Bulletin No. 127. • [August, 

2. THE ORIGINAL PLANT 

ORIGINAL HABITAT 

A. De Candolle (22 p, 46) states that Solanum tuberosum was 
unknown to the aborigines of eastern South America, although 
S. C ommersonii was common as a wild plant. Along the western 
coast, however, the potato was well known and its cultivation dif- 
fused from Chili to New Grenada. 

Pedro Ciega de Leon (86 p. 5) in his "Spanish Chronicles of 
Peru," makes the first written mention of the potato in 1550. 

"In the neighborhood of Quito," he says, "the inhabitants have besides maize, 
two other plants which serve as a great portion of their food, papas and quiniia. 
The papas has roots enlarged into tubercles, which are covered with a more or 
less hard skin ; these when cooked have a pulp nearly as tender as a puree of 
chestnuts. When dried in the sun to preserve them, they are called chumo, and 
are thus preserved for future use. The fruit produces a stalk similar to the 
poppy. The quiniia is a plant about the height of a man and has leaves like 
the blite of Mauritania, and a small seed either red or white in color, from 
which is prepared a drink, and a food comparable to our rice." 

Lopez de Gomara (86 p. 5) in his "Histoire generale des Indes" 
(11 54) and Augustin de Zarate in his "Histoire de la Decouverte 
et de la Conquete du Perou" (1555) also speak of this "papas" 
which is still the Indian name of the potato. Jerome Cardan in his 
curious work entitled "De Rerum Varietate" (Bale 1557) expresses 
himself in these terms on the same subject : 

"On the height of the mountains in the country of Peru, the papas are like 
a species of truffle which is served in place of bread, and are also dried in the 
sun. It is thus nature has wisely provided for all needs. When they are dried 
they are called ciuno. Certain people have found means to enrich themselves 
by transporting this commodity into Potosi. It is said that the root has a stem 
similar to that of Argemone. The papas have the form of chestnuts but have 
a more agreeable taste. They are eaten cooked or better as I said made into 
flour. They are found as commonly among other tribes of this peninsular as 
they are among the inhabitants of the province of Quito." 

Other writers through the latter half of the sixteenth century, 
and travelers and writers later, (22) show conclusively that the po- 
tato was and still is wild in Chili, but that the probability is that the 
plants found seemingly wild in Peru, were either escaped from cul- 
tivation or were allied species for which it had been mistaken. 

Introduction to Cultivation 

The Spanish conquerers of Peru introduced the potato into 
Spain and Portugal sometime between 1535, the date of the con- 



J9o8.] 



Improvement of the Potato. 



381 




Fig. I. The first potato introduced into Europe. From Clusius' Water- 
color OF 1588. (After E. Roze.) 



382 Bulletin No. 127. , [August, 

quest, and 1585, whence the cnUivation spread into Italy sometime 
early in the seventeenth century. From here, the potato in all prob- 
ability went to Austria, from Austria to Germany, Germany to 
Switzerland, and from Switzerland to France. 

Spanish voyagers also probably introduced the tubers to the 
English settlers in Virginia; at any rate they were being culti- 
vated there before 1585, and were sent to England at the time of 
Sir Walter Raleigh's voyages to Virginia though not by Raleigh 
himself. From England, potato cultivation spread very rapidly to 
Ireland which needed a cheap food crop, and by the beginning of 
the eighteenth century, it had become one of its staples. Their uni- 
versal use on the island from this time forward brought them their 
common name of the Irish potato. This nickname is not to be won- 
dered at for Ireland still leads in the use of potatoes with an annual 
per capita consumption of twenty-five bushels, or seven times that 
of the United States.* 

Two VxVKiKTiT'S Introduced 

We have seen that Bauhin wrote the first description of tlif 
potato in 1596, but as he in all probability received his specimen 
from Clusius, to the latter should be given the credit of the descrip- 
tion of the first cultivated potatoes. The specimens described by 
Clusius were sent to him in 1588 by Philippe Sivry, Seigneur of 
Waldheim and Governor of Mons, who had received them from 
Italy at the hands of the Papal Legate. The accompanying plate 
of Clusius is from Roze's colored plate made from the original and 
has not been available before in an English publication. Speaking 
of his reproduction Roze says : 

"This colored plate is a faithful reproduction from the most ancient docu- 
ment we possess on the introduction of the potato into Europe. For the orig- 
inal water-color which dates 1589 is kept with other writings and books of this 
epoch (of which the authenticity is certain) in the archives of the ancient six- 
teenth century printings and preserved in its original state at Anvers, Belgium, 
at the Musee Plantin-Moretus. The writing on the Latin manuscript which 
has also been reproduced from the original water-color is thus 'taratoufli a 
Philippo de Sivry acceptum Viennae 26 Januarii 1588. Papas Periianum Petri 
Cieqae,' and is a fac-simile of the writing of the celebrated botanist Charles de 
L'Ecluse of Arras, more commonly known to the world under his Latin name 
Clusius. 

"This proves to be, not the date of the reception of the water-color, repre- 
senting a flower stalk with two potatoes which had only been sent to Charles 
L'Ecluse in 1589 by Philip de Sivry, Seigneur dc Walhain et Gouverneur de la 
Ville Mons en Hainaut, but that of two tubers and one fruit berry of the 

*Mayo-Sniilli: Statistics and economics, p. 38. 



igoS.] Improvement of the Potato. 383 

potato that Carrolus Clusius Atrebatis, in his Rariornm Plantarum Historia 
published by Moretus in 1601, declared to have been sent to him by Philippe de 
Sivry a Vienne at the beginning of the year 1888. These tw^o tubers and the 
seeds from this fruit have produced all the potatoes which at the end of the 
sixteenth century were cultivated in Austria, Germany, Switzerland and France." 

Judging from this plate and from what Clusius says in his "Rar- 
iarum plantarum historia" (17), the plant has changed little under 
cultivation except probably to give few^er and larger tubers., The 
larger tuber shov^n in the figure is one and three-fourths inches long 
and would weigh about 35 grams. He states in his work that the 
plant then yielded as many as fifty tubers of unequal size and from 
one to two inches long. This would still be considered a good yield 
for a two-year seedling and is commonly not exceeded here the 
first or second year by unacclimated varieties imported from Europe. 

The other European introduction, — that into Great Britain, — 
was first described by John Gerard in his "Herbal," published in 
London in 1597. This has usually been given as the first descrip- 
tion of the potato and the accompanying figure is a reproduction of 
his wood-cut as given in the edition of 1636. Gerard, however, 
knew of Clusius' description as is shown in the following quotation. 
He says, speaking of the potato : 

"It groweth naturally in America, where it was first discovered as reporteth 
Clusius, since which time I have received roots hereof from Virginia otherwise 
called Norembega, which grow and prosper in my garden as in their own 
native country." 

It is remarkable that these two introductions into Europe were 
made with two different varieties of S. tuberosum. The one de- 
scribed by Clusius which probably produced the earlier varieties of 
northern Europe, had reddish tubers and light purple blossoms. The 
later introduction into England described by Gerard possessed light 
brown to yellowish tubers and violet to almost white flowers^ 

The variations in the descendents of these two varieties have 
been almost entirely restricted to the tubers. The ash-leaved varie- 
ties of England constitute an exception, where the variation is in the 
shape of the leaf. This fact is important from two points of view. 
First J it indicates that there has been but little correlated variation 
between underground and aerial parts, and hence we are unlikely to 
Und plant characters by zvhich zve can zvith reasonable CeTfainty re- 
ject unsuitable types. Second, zvith so little visible variation in the 
plant, there is likely to be narrozu variability in resistance to fungus 
diseases, should such resistance be due to structural differences. 



384 



Bulletin No. 127. 



[August, 






Fig. 2. The first potato introduced into England. (From woodcut in Ger- 
ard's Herbal. Ed. of 1636.) 



i9o8.] 



Improvement of the Potato. 



385 



3. THE MODERN PLANT 
Structure) and Characteristics 

The potato is an annual, and in its original state reproduced 
freely by seeds. The tubers were then so small that it is doubtful 
whether the plant would have been preserved to us by this alternate 
means of reproduction. At present, however, many varieties never 
or at most rarely seed, and the plant has become virtually a peren- 
nial through its tubers. 

Baker (6) gives the following technical description of a wild 
plant : 

"Leaves pseudo-stipulate, a fully developed one about half a foot long, 
with seven to nine finely pilose, oblong-acute, large leaflets, the side ones stalked 
and unequally cordate at the base, the one to two lowest pairs much dwarfed, 
leaving a naked petiole about an inch long; the rhacis furnished with numerous 
small leaflets interspaced between those of full size. The flowers arranged in 
compound terminal cymes, with long peduncles ; pedicels hairy, articulated 
about the middle. Calyx hairy, one-fourth to one-third inch long, teeth deltoid- 
cuspidate, as long as, or a little longer than, the campanulate tube. Corolla dark 
lilac, subrotate, nearly an inch in diameter, pilose externally; segments deltoid, 
half as long as the tube. Anthers bright orange-yellow, linear-oblong, nearly 
one-fourth inch long, filaments very short. Berry perfectly globose, smooth, un- 
der an inch in diameter." 

This description perfectly fits the cultivated potato of today, as 

Baker has already noted, with the exception that the lobes of the 

calyx are now a little more pointed. 




Fig. 3. 
a. Back side of anther. 



Parts of Potato Flower. 

c. Front side of anther. 



b. Pistil. 



d. Cross section of anther, 
e. Tops of anther showing the openings. 



\ 

386 Bulletin No. 127. [August, 

The flowers in the cultivated plants vary in color from white 
to purple, and usually two clusters growing side by side make up 
the compound cyme. They possess an entire, five pointed corolla 
with five stamens with large fleshy anthers enclosing the pistil. 
Darwin quotes Makenzie (68) as describing a variety which pro- 
duced two sorts of flowers, the one double and sterile and the other 
single and fertile.' The sexes mature at the same time; the anth- 
ers open at the top like a small cup, and in certain cases split for a 
short distance. The pollen is usually wind carried, as the flowers 
produce no nectar and are not greatly frequented by insects. Miiller 
(75 p. 425) and Fruwirth (43 v. 3 p. 6) each mention several spe- 
cies, however, that they had noted around the flowers. Darwin 
considered self-fertilization possible; and from the comparative 
ease with which I have obtained "selfed" fruits in twenty-six dif- 
ferent varieties, and from the rarity of insect visitors, I believe self- 
fertilization to be natural to the species. The flowers open between 
five and six o'clock a. m. in this climate and slightly close about 
dusk. The pollen is usually shed on the second day of blooming 
and it is then that the pistil is most receptive. With profuse seed- 
ing varieties the flowers wither about the fourth day. 

Fraser (37 p. 5) states that out of three hundred varieties many 
of which he has grown for several years, he has found none which 
do not bloom at some time of their life. In opposition to this view, 
Rev. J. R. Lawrence, of North Middleboro, Massachusetts, who 
grows some eight hundred varieties asserts that some varieties 
never bloom. However this may be it is certainly true that there 
is a great variation in varieties in the power to bloom and still more 
in their ability to set seed. Some varieties evidently go for years 
without blooming, others bloom whenever there are optimum condi- 
tions of climate and season. I have found varieties setting seed 
freely in Waupaca county, Wisconsin, when during the same season 
plants from the same fields of the year before produced no seed 
in Champaign county, Illinois. There are varieties which develop 
clusters of buds which fall without opening^ and many more which 
produce flowers, all of which fall without setting fruit. Some of 
the anthers in the latter varieties contain no pollen, others shriveled 
pollen grains containing no protoplasm, while still others produce 
viable pollen though never (in my experience) in large quantities. 
The blossoms separate at certain fixed places on the stem where a 
ring is formed by layers of tissue drying. Liebscher (66) states 
that fragrance is correlated with yield of pollen but I have found 
no noticeable fragrance in American varieties. 



iQoS.] Imtrovement of the Potato. 387 

It is a common idea that the potato does not set fruit as freely 
now as formerly, and the explanation has been given that the pro- 
duction of large quantities of tubers has led to the degeneration of 
the seeding power. It is true that many of our finest varieties 
bloom seldom and rarely set seed, yet this does not seem to be a cor- 
relation with yielding power, for some of our best varieties bloom 
freely, and under proper conditions, set seed. 

Fraser (37) has shown this variation in blooming to have been 
natural nearly two hundred years ago. He says : 

"Mark Catesby, who was in this country in 1722-1726, wrote that 'in Vir- 
ginia and to the north thereof, they (potatoes) are annuals, and produce no 
flowers, while in Carolina and the Bahama Islands, they produce flowers. Many 
varieties existed at that time particularly in Virginia, and five kinds were com- 
mon : the Common, Bermudas, Brimstone, Carrot and Claret potatoes. The 
Bermuda potato was the only one that had a white flower, the flowers of all 
the other kinds being purple. This was the only variety that had a white skin 
and was white fleshed. It was round in shape, more tender, and more delicate 
to raise than the others, and did not keep so well." 

In Connecticut, many excellent varieties do not seed and cannot 
be used as stock to breed from, but varieties representing all of our 
favored commercial variations in shape and color, can be obtained 
which produce seed. In other climates, notably Maine, Minnesota 
and Wisconsin many of the non-seeding varieties of Connecticut 
produce pollen and seed comparatively freely. This makes it pos- 
sible to obtain hybrid seed from varieties where the female parent 
at least is acclimated and adapted to these soils, for the female or- 
gans appear to be always perfectly normal. 

The tuber of the potato is a swollen, underground stem, with 
its eyes equivalent to the leaf buds of an aerial stem, and which are 
arranged more or less spirally in each case. The main underground 
stem of the plant varies in length with the depth of planting. At 
intervals on this underground stem, stolons are sent out, at the ex- 
tremities of which are found the tubers. Varieties differ greatly in 
the length of these stems and the manner in which the tubers are 
formed. A variety to be of commercial value should have very 
short stolons and bear only one tuber at the end. There should be 
no branches from the bud end of the tuber, as is sometimes the case. 

The physiology of tuber formations is discussed at length by 
Vochting (loi). 

Varieties oe Today 

At present, there are in the United States over one thousand 
named varieties. This large list contains many names that repre- 



388 



Bulletin No. 127. 



[August, 



sent potato plants and tubers having the same characteristics, and 
which are indistinguishable, even to an expert potato buyer. In 
some cases this has been due to the actual stealing of meritorious 
varieties by unscrupulous dealers, who have put out the stock under 
a different name, and given it a foothold by persistent advertising. 
More often, however, the duplication has been done by potato fan- 
ciers who are growing seedlings from naturally pollenized seed, and 
who obtain similar strains which are saleable to seedsmen, as new 
varieties for the single reason that they have been obtained from 
seed. If the yield is fair, and the tuber is of a popular type, the 
restless fancy of the American public for something new, gives a 
ready, though temporary market for the stock from the new seed- 
ling no matter if it is slightly inferior to its already established 
prototype. I have seen at least twenty named varieties of the Car- 
man No. 3 type (short-oval-flat with white skin) which were ab- 
solutely indistinguishable in shape, color, and manner of growth, 
and if the popularity of this type continues there will undoubtedly 
be an annual addition to this list of names. 

Of real variations in varieties, productive efficiency or ability to 
excel in crop production under like conditions of environment, is 
the character of greatest importance at present to the grower. The 
astonishing adaptability of some varieties as compared to others, 
to certain soils and climates is shown in the following table from 
varieties grown at the Connecticut Agricultural Experiment Station 
in 1906, on plots of poor but uniform soil with like treatment as 
to planting, cultivation, fertilizers, etc. To what these differences 
are due: whether there are many different elementary species in 
S. tuberosum whose characters have been recombined into innumer- 
able varieties by hybridization; or whether they are due merely to 
desirable fluctuations that regress slowly because of bud propaga- 
tion is unknown. The fact of the differences remains. 



Table i. Variation of Varieties in Productiveness under Uniform Field 

Conditions 



Variety. 


Yield per acre in bushels. 




Marketable. 


Seconds. 


E. Six Weeks 


18.7 

36.2 

57.2 

74.7 

79.3 

102.7 

113.2 

137.7 


8.2 
11.7 
30.3 
23.6 
14.0 
11.7 
17.5 
^18.7 


E. Ohio 


E. Norther 


Minister 


E. Manistee 


Twentieth Century 

State of Maine 


Green Mountain 





IQOS.] Improvement of the Potato. 389 

Owing to the great local differences in soil fertility and physical 
character, this character of productiveness must be determined by 
trial in every climate and for every soil. It is pre-eminently the 
desired character of the grower, as all other characters are at 
present, more or less fancy demands of the consumer, and concern 
the grower only so far as the urgency of the demand affects the 
price. Some of the characters that generally receive attention from 
modern growers as conducive to, or correlative with, yield, — are 
disease resistance, character of haulm and leaf, time of maturity, 
and length of stolons. 

The first character is well discussed in a recent publication of 
Jones (59). In the writer's experience there is certainly a varia- 
tion in the ability of different varieties to resist attacks of early and 
late blight, but whether the differences noticed zuifhin the variety are 
due to anything but a different time of infection is ciuestionable. 
That there are wide individual variations in respect to susceptibility 
toward the physiological trouble, tip burn, is more apparent. 

The haulm should be vigorous, covering the ground when in 
full growth, but upright and bushy rather than long and sprawling. 
The meeting of the plants in the row conserves the soil moisture 
when cultivation can no longer be given while an upright, bushy 
haulm favors ease in the farm operations, and probably tends to 
lessen disease infection. 

In general, varieties yield in proportion to their growing sea- 
son, provided there is entire maturity before frost. Varieties which 
are still green at the close of the season have large numbers of tu- 
bers set but a great many of these fail to reach a marketable size 
and the plant is killed while still containing much dry matter which 
should have been transferred to the tubers. Length of stolon seems 
to be a very strong variety characteristic and permanent when ob- 
tained. The length should never exceed three or four inches, al- 
though with S. Commersonii, it sometimes reaches the extreme 
length of ten feet. 

Variety characteristics which are prominent and which depend 
almost entirely on the public taste to be of value, are those of tuber 
shape and skin character. There are varieties possessing every pos- 
sible shape, but they may be roughly divided into the oval and the 
round and, if we wish to make a third class, the kidney shaped. 
The popular shapes at present are quite flat, the short-oval-flat be- 
ing the most desired. There may be a sufficient reason for this, as 
Fischer (32 v. 2 p. 49) found that flat-round tubers or flat-oval 
tubers showed a correlation with starch content. The actual reason 
for popularity would seem to be the fact that potatoes of this shape 
give a greater weight per measure, in which manner they are usu- 
ally retailed. The eyes of potatoes of this type are also compara- 
tively shallow, thereby giving less waste. 



390 Bulletin No. 127. [August, 

Skin color seems to be purely a matter of preference without a 
real reason, there having been no correlations shown between par- 
ticular colors and other desirable qualities. White to light brown 
are the colors most sought in the northern markets while red 
skinned varieties find ready sale in the south. Krzymowski (63) 
states that rough skinned varieties are highest in starch content ; 
and it is generally believed that this is also correlated with re- 
sistance to scab. 

Modern Potato Breeders 

Growing potato seedlings has been a fascinating work for 
thousands of gardeners throughout the United States, who have 
taken up the work merely as a recreation and have planted seeds of 
unknown parentage, rejecting year by year those which gave poor 
yields or had characteristics which were thought undesirable for 
market. The mere fact of numbers has brought from this desultory 
work a large number of commercial varieties, a conspicuous ex- 
ample being the Burbank potato. This variety was the progeny 
of a natural seed ball found in a garden by Mr. Luther Burbank 
when he was a boy. As we only hear in such cases from those 
who are successful, there is no way of judging the percentage of 
failures ; but judging from those who have come to my personal 
knowledge, and from talking with seed merchants, certainly not 
over one or two percent of these growers ever produce a commer- 
cial variety. Varieties which come into prominence today show 
increasing evidence of the work of the breeder who studies his 
ground carefully and works toward a definite end. It is probably 
not too much to say that 90 percent of our present potato crop is 
from varieties originated by scientific breeders, such as the late 
E. S. Carman. The small amount of published matter concerning 
the present day workers in potato breeding and their methods 
makes correspondence necessary for organized work, and a list of 
some of the prominent workers is given here. 

United States : O. H. Alexander, Charlotte, Vt. ; Marvin Bovee, North- 
ville, Mich. ; E. L. Coy, West Hebron, N. Y. ; W. E. Johnson, Bowdoinham, 
Me.; J. R. Lawrence, E. Raynham, Mass.; Chas. Norcross, Litchfield, Me.; C. S. 
Pringle, Charlotte, Vt. ; Hiriam Presley, Port Huron, Mich.; E. L. Roser, 
Cleveland, O. 

Great Britain: James Clark, Christ Church, Hants; Robert Fenn, Holm- 
wood, Sulhampstead, Reading; C. Fidler, Reading; A. Findlay, Markinch ; T. A. 
Scarlett, Edinburgh ; A. W. Sutton & Son, Reading. 

France: Tibulle Collot, Maizicres ; Forgeot & Cie., Paris; Leonard Lille, 
Lyon ; Hyacinthe Rigault, Groslay ; Joseph Rigault, Groslay ; Vilmorin-An- 
drieux et Cie., Paris. 

Germany: Cimbal, Fromdorf bei Miinsterberg; Flieszbach, Curow, Pom- 
mern; A. Kirsche, Pfiffelbach; von Lochow, Petkus; G. Rlodel, Tagewerben 
bei Weiszenfels. 



iQoS.] Improvement of the Potato. 391 

4. METHODS OF BREEDING 
General Basis 

In potato breeding-, there are four steps before the worker: 
I. Selection of varieties for improvement. 2. Discovery of valuable 
bud-variations. 3. Selections of mother plants, and their crossing. 
4. Comparison and selection of the progeny. It is the province of 
the breeder to discover the best methods for prosecuting this work, 
— the obstacles in the way, and the probabilities of success under 
different conditions. The means of propagation of the potato is in 
most of these steps a disadvantage. The comparatively simple 
methods of the seed propagated annuals and biennials are seri- 
ously complicated, and the advantage of grafting held forth by the 
orchard fruits is lacking. 

In taking the first step, it is in some cases impossible to select 
varieties with characters that are desirable, to combine with those 
possessing other characters, because of the large number of varieties 
which produce no viable pollen. A great number of varieties must 
be grown, and the matter as to whether fertile pollen is produced 
in quantities large enough to make hand pollination practicable 
must be determined during their comparison as varieties. It has 
been held by many horticulturists since the time of T. A. Knight 
(60) that varieties which did not bloom readily could be stimulated 
into fruiting by removing the soil from the underground stems, or 
otherwise preventing the production of tubers. This does not seem 
to be true at present with American varieties, for with ten different 
varieties in Connecticut and with five in Illinois, we obtained by 
this method no natural seed balls, and by microscopical examination 
found no seeming increase in production of viable pollen. At least, 
we might conclude that the reaction to this means is not certain 
enough to be of great value to the breeder, and seed producing va'- 
rieties must be selected zuhich come nearest to the ideal in the char- 
acters needed. Some hybridists select parent varieties of similar 
type with the idea of improving qualities already obtained, while 
others cross widely divergent types, with the hope of obtaining a 
smaller percentage of seedlings with much better characteristics. 
Doubtless both methods are necessary, if it is certain in all cases 
that there are eminently desirable characters in the types used. 

Having selected the varieties with which to work, it is of doubt- 
ful value to use any of the old-time horticultural methods, — such 
as over supply of food materials, — to induce variation. We may in 
the future learn to use artificial means to produce mutations, but 
the "plus" fluctuations induced by food supply are probably abso- 
lutely valueless when we are about to resort to sexual reproduction 



392 



Bulletin No. 127. 



[August, 



in the origination of new types. But, even if artificially produced 
fluctuations were heritable, there would be no necessity for their 
production; for, owing to the hybrid character of the greater 
number of potato varieties — or for other reasons — the natural 
variation of seedlings is very great, even when they are the product 
of crosses within the variety. Foreign varieties may very properly 
be grown until they are fully acclimated; that is, until the varie- 
ties are growing with full vigor. During the first year or two such 
varieties seldom flower; and even if they do, the flowers fall more 
quickly than they do with vigorous plants, and hybridization is ef- 
fected with difficulty. 

There is also some doubt as to the value of bud variations, but 
pending further investigations, we should watch for any such oc- 
currences. Data soon to be published by the writer seem to indicate 
that progressive mutations, that is, the appearance of an entirely 
new character, rarely and possibly never, occur. Bud variations 
are in nearly all cases merely the loss of a dominant character leav- 
ing the recessive allelomorph to appear. Such variations are not 
likely to be of great economic value. 

The selection of individual plants to be crossed is still a matter 
of personal opinion and experiment. While we may not believe in 
the heritability of vigor occurring as a fluctuation within a variety ; 
still the greater ease of making crosses between vigorous plants is a 
sufficient reason for their selection as mother plants. The latter is 
due to the greater probability of their retaining the seed ball to its 
maturity. 

Girard selected plants having the most luxuriant vegetation, 
and according to T. A. Scarlett (88), the same method is practiced 
in Scotland. We have found that there is a great difference in 
varieties, as regards the value of luxuriant vegetation as a guide 
in selecting high yielding plants. Large vines versus medium vines 
gave fair results in most cases ; but in some varieties as Manistee, 
large vines rather indicated that excessive vegetative growth was 
opposed to maximum tuber formation. 

Table 2. Selection of High Yielding Plants by Size 



Variety. 


Average vine production 
in ounces. 


No. counted 
of each. 




Large vines. 


Medium vines. 


Pink Gem 


21.5 
24.1 
22.1 
16.0 
16.6 


14.25 

19.3 

20.0 

16.1 

16.9 


50 
50 
10 
10 
10 


Sir Walter Raleigh 


Carman No. 3 


Early Ohio 


Karly Manistee 





JQ08.] Improvement of the Potato. 393 

There is no constant difference due to selection of plants with 
a single stem and those which branch just below and just above the 
ground, providing they are equal in top weight and that it is cer- 
tain that the branched selections are single plants. There appears, 
however, to be an optimum shade of color in vines, constant with 
the variety, which is correlative with, or a result of vigor in the 
plant. Lighter colors gave fewer potatoes although these were of 
good size, while darker colors either gave no set of tubers or a 
large set of very small tubers. The latter condition sometimes 
seems to be due to a very late setting of tubers in late varieties, 
leaving too short a season for the tubers to mature. 

* The actual crossing of the plants selected is a simple matter. 
The corolla and stamens of the selected blossom of the mother 
plant should be cut away before it is fully developed, and the blos- 
som then bagged with a small waxed paper bag. When the stigma 
is receptive (sticky), dust on the pollen collected from the "sire" 
plant with a camel's hair brush. This pollination should be repeated 
on two successive days, if the pistil has not fallen. It is better to 
limit the fruits of the mother plant to two, but several flowers 
should be pollinated in order to stimulate growth in the peduncle 
of the cyme. When the fruit has begun to form, remove the bag 
to allow free access to air and light. When the fruits are ripe, they 
are gathered and allowed to dry. It is better for their viability to 
squeeze out, clean and dry the seed, rather than allow them to stay 
all winter in the berries where there is an opportunity for decay. 




Fig. 4. Irregular cyme of potato flowers. One ready for pollination. 



394 Bulletin No. 127. • [August, 

The seed is planted in a hot house in -February and transplanted 
twice before planting in the open after danger of frost is over. 
Fraser (37 p. 174) believes the old idea of this first year crop con- 
sisting of small tubers does not always hold and states that a 
tuber weighing over seven ounces has been grown the first year. 
He says, "The Burbank potato was full size the first year it was 
grown from seed, and many breeders feel that unless the tubers are 
of edible size the first year that they are not likely to be worth fur- 
ther care," Girard (45) also states that with proper cultivation, 
seedlings will produce marketable tubers in one or two years. 

I have seldom seen a marketable tuber produced by even a two 
year seedling, and think that such results must be unusual. The 
vines certainly often reach full size the first year, but the growth is 
almost entirely vegetative with very little matter stored in the 
form of tubers. The vines producing the larger tubers seldom pro- 
duce a large number, and I have been told by several reliable breed- 
ers that they prefer, — the first year as well as subsequent years, — • 
to select the vines having the largest number of tubers. And while 
there are no comparative data, the use of the plant as a whole as a 
selective unit appears the more reasonable. The great majority of 
the seedlings produce tubers of only one to fifty grams weight the 
first year and require three years to reach their full size. It is also 
noticeable that the typical shape of the strain is not generally 
shown the first year, the tubers at this time generally being round 
in shape. 

Precautions in Comparative Tests 

After the first year the elimination of the unfit begins. The 
tubers from the year before are compared in the garden in short 
rows and as elimination goes on the best are given field trials. In 
carrying out all field and garden comparison tests, there are a great 
number of factors which have an influence upon growth, and which, 
as far as possible, must be taken into account; for a field test at 
best has a large experimental error and the error with potatoes is 
probably larger than with any of the seed propagated annuals. 

The more common operations of all field experiments which 
first come to mind and which scarcely would be neglected in the 
comparison, are absolute uniformity in the time of planting, num- 
ber of times and methods of cultivation and spraying, kind and 
amount of fertilizer, and time of harvesting after dividing the va- 
rieties into early, medium and late maturing. There are a number 
of other points which have been neglected in far too many potato 



igoS.] Improvement of the Potato. 395 

investigations. A common error, as Thome has pointed out (97), 
is in disregarding the type and typography of the soil. The soil 
should be as uniform as possible, preferably of sedentary origin, 
and previous to its experimental use, should have been fertilized 
and cropped in exactly the same manner. The land should be 
slightly rolling and the potato rows should run up and down the 
declivity so that the comparison of the whole rows is perfectly fair. 
Water is a very important factor in potato growing, and small 
depressions in flat lands receive an unequal portion of the surface 
drainage which vitiates the results. 

E. Pagnoul (yy) attributed the large yield of potatoes in sea- 
sons when the total hours of sunshine were large, to the effect of 
light on elaborating starch. His results may be slightly distorted 
as he reports only a portion of the conditions which enter into his 
experimental error, but results as reported gave a ratio of approxi- 
mately I :5 :ii for plants under darkened glass, clear glass and open 
air respectively. Therefore precaution should be taken concerning 
all shade. 

Results from numerous experiments, among the most accurate 
of which are those of Maw (74) and Plumb (82), have shown that 
much care must be taken to have equal weight of seed planted, for 
other conditions being equal, the yield of tubers increases directly 
with the weight of the seed piece although not exactly proportional. 

Arthur (2, 3) and others have pointed out a difference in yield 
owing to the difference in age and vigor of eyes sprouted before 
planting. Wilting tubers up to a loss of moisture of 20 percent also 
increased growth. He advances the proposition that : "Whatever 
increases rate of growth at the beginning, increases yield." Finally 
Gilmore (44) has shown that depth of planting certainly affects the 
quality and on certain soils the yield; while Clinton (16) suggests 
that it may also cause a difference in time of infection with Phy- 
tophfhora infestans. 

These factors can probably never all be controlled in the same 
experiment but they should all be kept in mind, and all reasonable 
effort made to lessen errors due to them in comparative tests. 

CoRREIvATIONS 

Many so-called correlations of characters have been observed 
by different investigators. These correlations are said to be some- 
times very marked,' and of great value in making selection 
where one of the correlated characters is easier to select from 
than the other. The physiological reasons for many of these ef- 



396 Bulletin No. 127. . [August, 

fects are obscure, and there appears to be no certain way of dis- 
tinguishing between what might be called real correlations, which 
are probably to a greater or less degree effects from the same in- 
ternal cause, or where two characters are inherited as a single unit : 
and false correlations in which one is the cause and the other the 
effect, or in which both characters vary as the result of some ex- 
ternal stimulus. In practical work either type may become a help 
in its prosecution, but in studying problems of heredity, inability to 
distinguish the type often leads to great confusion. Space cannot 
be taken to comment upon these observations except to make the 
statement that it has been the writer's experience that the degree of 
correlation of any characters which he has observed, is extremely 
variable with different varieties, on diverse types of soil, and in dis- 
similar seasons. 

With regard to the production of plants, Arthur (2) in an 
elaborate investigation found that the number of stalks is very 
slightly if at all related to the number of eyes upon the seed piece, 
provided pieces of equal weight are used. The number of stalks, 
however, increases directly with the weight of the seed piece; and 
with the number of stalks varies directly the number of tubers and 
their total weight in the produce. He also and later Wollny (112) 
state that the eyes of large tubers produce stems of a sturdier 
growth. 

Liebscher (66) states that thin stemmed plants produce small 
tubers and that plants with fine stems produce many small tubers. 

There seems to be no constant relationship between colors of 
tubers and of blossoms or between dark skinned tubers and dark 
vines, but Liebscher (66) found that profuse blossoming points to 
late ripening, and heavy seed setting to small tuber formation. The 
latter statement has been a general belief but Fraser (37) states 
that in his experience many of the heaviest yielding varieties at 
least bloom freely. Liebscher believed seed and tuber production 
to be physiologically opposed. Fruwirth (43 v. 3 p. 10) states that 
Dalkowsky is of the opinion that strong power of seed production 
is also correlated with ability to resist disease. 

Osterspey (76) found in early varieties less foliage than in late 
varieties; and within a variety, in both early and late varieties, 
there was a relation between number of tubers and number of 
stalks. 

Fischer (32) found that flat-round tubers were richer in starch 
and produced less massive plants; while long-cylindrical tubers 
were poorer in starch and produced large straggling foliage. Fru- 



igo8.] Improvement of the Potato. 397 

wirth (41), in three years' observations with both early and late 
varieties found a relation between yield and the following charac- 
ers : Flat shape, number of stalks per plant, length of growing 
period, height of plants and number of tubers per plant. He also 
states that the greater the number of stalks from a plant, the 
thinner are the stalks. 

Some of these correlations may help materially in eliminating 
some of the undesirable plants from the progeny of crosses from 
which we are trying to build up new varieties. There may also be 
many pairs of characters with high percentage correlation which 
have not yet been noticed but which will be brought out with 
further statistical studies. It is doubtful, however, if many of 
these characters which appear to be related in certain varieties, 
are to be regarded as real correlations characteristic of the species.' 
Reasoning from statistical studies of the writer on maize and sugar 
beets, which may or may not be analogous, it would seem that cor- 
relations which are likely to be of most practical value in making^ 
selections will probably be found in very narrow blood lines (ele- 
mentary species?). For example, in ear-to-the-row tests of dent 
maize there was planted an ear with a peculiarly shaped tip. This 
ear yielded very highly, and of its progeny when grown and their 
yield compared, in nearly every case, those were found to average 
highest whose mothers had this peculiar tip. 

In hybridization, pairs of characters may be found which are 
inherited as a single character. When both characters are desir- 
able, this would be a decided help, but when one character is unde- 
sirable, there is only the consolation of knowing the difficulty of 
finding exceptions to the rule. Johannsen (58) states however 
that, "Crossing is the means of breaking the correlation." 

In selection, those correlations are of greatest value which al- 
low us to eliminate plants through correlations of characters in the 
young vines, with characters in the tubers. It is doubtful, however, 
whether weak correlations should be used in originating varieties. 
They are probably of practical value only when the life history of 
the variety is known. 



Bulletin No. 127. - [August, 

5. INHERITANCE OF CHARACTERS IN TUBER 
SELECTION 

Theory 

We do not mean by this term the inheritance of the characters 
in future sexual crosses, but the transmission of selected variations 
from year to year by tubers. A consideration of this question is 
of practical importance to the potato grower. The potato breeder 
may still continue to make crosses and originate varieties, but in 
such work he is and must be a specialist. His work can never be 
undertaken with profit by the average grower, to improve his stock. 
On the other hand, if there is a possibility of selecting and propa- 
gating favorable fluctuating variations and their accumulation for 
ihe betterment of the variety, such work can be undertaken with 
success and profit by the farmer. 

It is common knowledge that during the first few years the 
progeny of a sexual cross in potatoes is quite variable. These 
variations may be arbitrarily divided into two classes : First, those 
variations that seem to be due directly to slight differences in en- 
vironment, such as shape, size and yield of tubers, and vigor of 
growth and amount of foliage in plants ; second, variations that 
are much rarer and that seem to be of a more nearly botanical char- 
acter as those of color tubers, length of life of plant, and amount 
of blossoms and production of seed. Variations, in the after life 
of the variety are said to become less common, that is, the type of 
the variety is said to become fixed. This appears to be true from 
general observations of potato seedlings, and it might partially be 
explained by the fact that each year the plants are subject to rigid 
selection to a certain type. // these fltictuations are transmitted, 
the plants dealt with in subsequent years are a selected and not a 
general race. But when unselected it is probable that there is 
a lessening variability with advancing age, even when the physio- 
logical vigor of compared plants is kept the same. Vernon (99 p. 
184) showed conclusively that for low forms of animals as the sea 
urchin that the "Permanent effect of environment on the growth of 
a developing organism diminishes rapidly and regularly from the 
time of impregnation onwards." A little later De Vries (26) enun- 
ciated practically the same law for plants. He concludes: i. The 
younger the plant, the greater is the influence of external condi- 
tions on its variability. 2. The nutrition of the seed when develop- 
ing on the mother plant has (at least very often) a greater influ- 
ence on the variability than during germination and growth. 



iQoS.] Improvement of the Potato. 399 

Hence if we consider a potato variety as a perennial individual, 
though divided, we may conclude that following these laws the 
variability lessens as the variety becomes older. 

Admitting this law to be sufficient reason for lessened variation 
in the variety as it ages; there is still variation, and as Bailey (4) 
has shown considerable variation, both continuous and discontinu- 
ous, or with De Vriesian names, both fluctuations and mutations. 
In the progress of evolution, such variations must have been suf- 
ficient either as mutations or as accumulated fluctuations to have 
created varieties and even species. In no other way could the 
numerous species and varieties of the asexually propagated fungi 
have originated, as well as numerous varieties of higher plants of 
various families, as sugar cane, banana, weeping willow, sweet po- 
tato, olive, fig and date which seldom or never are propagated by 
seeds. But as most biologists now accept the doctrine of discontin- 
uous evolution we cannot a priori conclude that partial fluctuations 
(using the terms described below) are inherited even in the tem- 
porary Galtonian way in which individual fluctuations are inher- 
ited. De Vries (27) divides fluctuations into two heads which he 
says "obey quite the same laws," but which with respect to ques- 
tions of heredity should be carefully separated. "They are desig- 
nated by the terms 'individual' and 'partial' fluctuation. Individual 
variability indicates the differences between individuals, while par- 
tial variability is limited to the deviations shown by the parts of 
one organism from the average stature." Fluctuations, he says, 
take place in only two directions, the increase or decrease of what 
characters are already available, and in this way are fundamentally 
different from mutations which take place in all directions, and if 
progressive produce new characters. He concludes that partial fluc- 
tuations are usually far smaller than individual and partial fluctua- 
tion together, and that partial variations do not appear to offer im- 
portant material for selection.* Multiplication by buds, however, 
of high extremes of individual fluctuation, he says, is what the 
breeder desires to obtain. 

From De Vries' work, we might conclude that although partial 
fluctuations obey the same laws as individual fluctuations, there is 
not a great chance for improvement through their selection, because 
of their narrowness. Theoretically the fluctuations of the whole of 
any variety of potatoes belong to this class. Still the variability 

*De Vries, however, admits the possibility of the commercial value of the selection of par- 
tial variations, when he savs (P. 7b0i: "Potatoes for the factory have even been selected for 
their amount of starch, and in this case at least, fluctuating' variability has played a very im- 
portant part in the improvement of the race." This is an admission of something that cannot 
be regarded as an undisputed fact. — E. M E. 



400 BuLivETiN No. 127. , [August, 

should be greater in the potato than in parts of perennial plants 
from a single rootstock, — from the latter class of which De Vries 
obtained a great deal of his data, — on account of greater diversity 
of environmental forces. The variation here ought to be analogous 
to the individual fluctuations of the fungi, or asexual animals which 
have the power of obtaining food in different places and of being 
surrounded by diverse conditions. 

A study of the actual amount of difference of fluctuating vari- 
ability in asexual and sexual reproduction has been made by Pear- 
son (80), who also makes use of Warren's (102) work on parthen- 
ogenetic reproduction in Daphnia. Their work makes use of datg. 
from both animals and plants which might be criticized as not be- 
ing strictly comparable, although most great biological laws have 
thus far seemed to apply to both animals and plants. 

His first proposition is that selecting one parent reduces the 
variability of the race by only about 5 percent while selecting both 
parents reduces it about 10 percent, and this is almost the limit of 
reduction even if the whole back ancestry be selected. The varia- 
tion then taking place is, of course, from the new type and not from 
the unselected type. 

This proposition if true for such reproduction* as there is in 
potatoes, would show the probable amount of reduction of varia- 
bility which there is in the established variety after it has been 
selected to type for several years and then placed on the market, 
leaving out of consideration the lessened variation due to greater 
age in the variety. 

The next point is that the individual-]- variability in a fluctuating 
character after a bi-sexual union is not greatly less than the varia- 
bility of the race. As an example, is taken the number of stigmatic 
bands on the capsules of Shirley poppies. The racial variability is 
1.885 bands, the individual variability based on 300 plants is 
.8518x1.885, or a reduction of 15 percent. Again, the racial varia- 
bility of the number of leaflets on the compound leaf of the ash was 
found by examining two hundred trees to be 1.976; the partial 
variabihty is .9181x1.976 or a reduction of only 8 percent.* * 

The last point is made on the variability of mothers and daugh- 
ters in the purely asexual reproduction of Daphnia. The variability 
of the mothers for a certain character was 2.221, for their daugh- 

*This fact should be true at least for selectiou from orosses. 

tPearson does not distiug-uish here as does De Vrics between indidividual and partial fluct- 
uations. ' 

**The writer does not subscribe to all of Pearson's conclusions on homotyphosis. There 
are, however, certain fluctuating' characters where the individual variation'is probably' but 
little less than that of the race. 



iQoS.] Improvement of the Potato. 401 

ters 2.950; for the array of daughters due to a mother of given 
character^ an average of 2.610. Even after considering that moth- 
ers are a selection and not a race, the following conclusions are 
drawn : 

,(i) "In asexual reproduction an individual does not produce a facsimile 
of itself, and the variability of its offspring is not immensely reduced belowr the 
variability of the race. 

(2) The asexual individual has offspring exhibiting regression, just like 
the sexually reproductive individual. Its offspring tends to regress from the 
individual to the race type. 

(3) With high probability but not definitely, the asexual individual repre- 
sents the mid-parent (i), i. e. .466 and .619 are well within the probable errros 
of the values .424 and .600, which we have found (Grammar of science p. 471) 
for the correlation and regression of the mid-parent in the case of the bi- 
parental inheritance." 

Summing up the whole case, he says : 

(i) "Whatever be the physiological function of the sex in evolution, it is 
not the production of greater variability." 

(Note) This does not mean that sex is not a great factor in 
producing a great variety of forms by combinations of existing 
diverse characters, but these differences must exist in the parents 
or previous ancestry of the individuals producing this combination. 

(2) "The variability of the individual makes itself felt not only in the bi- 
parental reproduction but in autogamic and parthenogenetic reproduction, and 
further in the undifferentiated like parts of the same individual. 

(3) Whatever amount of selection has taken place, there seems no possi- 
bility of reducing variability beyond some 10 percent or 11 percent." 

From the evidence given above, it seems reasonable for us to 
make the following conclusions as a working basis for our own 
problems. First, that there is fluctuating variation in asexually 
propagated vegetation which when reduced to a basis comparable 
to sexually propagated plants, is not to a great degree inferior. Sec- 
ond, that decreasing variability in a potato variety need not be due 
to a fixation of type which presupposes an inheritance of fluctua- 
tions. It may be explained by the decreased reaction to environ- 
ment of an aging individual. Third, that, if partial fluctuations 
obey the same laws as other fluctuations, types may be changed by 
their selection ; and this selection reduces the variation of the char- 
acter in the neighborhood of 10 percent. 

Our whole problem is reduced to the question whether types 
may or may not be changed by the selection of fluctuations. If 
types may be changed by the selection of individual fluctuations, 
they may likewise be changed by the selection of partial fluctuations. 
Until recently an affirmative answer to this theorem would not have 



402 Bulletin No. 127. . [August, 

been questioned. All of our conclusions, however, have been based 
upon the supposition that the data obtained in experiments with 
fluctuations, were obtained from homogeneous material. Johann- 
sen's (58 a, b) work has thrown into considerable doubt the homo- 
geneity of natural populations. He has, moreover, concluded that 
the selection of fluctuations has nothing to do with the improvement 
of a race. Probably no other conclusion of recent times is so im- 
portant to plant breeders. The work should certainly be duplicated 
along as many lines as possible; for its corroboration would not 
only sound the death knell of methods of improvements by the se- 
lection of partial fluctuations, but would entirely change our con- 
ception of procedure in other breeding operations. 

Johannsen's experiments were made upon typical fluctuating 
characters, such as weight and length of seeds. The plants used 
were species, like beans, that could be self-fertilized during suc- 
cessive generations. All of the descendants of a single plant, aris- 
ing by self-fertilization, he speaks of as a "pure line." The mem- 
bers of a pure line were distributed normally around a modal or 
type value in the case of each character considered. Likewise, all 
seeds from plants of the same variety, made up of a large number 
of pure lines, showed a normal variability. Some of the modal 
values of the pure lines were very close to the modal value of the 
variety, while in other pure lines the modes were quite different 
from it. When any individual, differing widely from the mean 
value of its pure line, was selected for propagation, its offspring 
showed almost a complete regression to the type of its particular 
line ; but showed no regression whatever to the type of the variety. 
He concludes, then, that a natural variety consists of a larger 
or smaller number of distinct types, each type having a distinct 
modal value for particular fluctuating character. These distinct 
types he calls "biotypes." Only by mutation or some rearrange- 
ment of characters can a pure line come to contain more than one 
biotype. If such a phenomenon takes place, the new biotype can 
be isolated, and remains true until another mutation or rearrange- 
ment takes place. It is quite clear that the only role of selection is 
to more or less completely isolate the different biotypes of a variety, 

Johannsen leaves out of consideration forms of vegetative prop- 
agation; though for what reason I cannot understand. Tuber re- 
productions in potatoes is a form of reproduction in a pure line. .If 
these conclusions are wholly warranted, — and Johannsen's work is 
extremely careful, — no improvement can be made by selecting plus 
fluctuaiiuiis in potatoes, except upon the intervention of mutative 



n 



IQOS. 



Improvement of the Potato. 



403 



changes. That mutative chang-es do take place, we are certain ; but 
nothing is known of their character or frequency. I beHeve that po- 
tatoes are very good material with which to throw some light upon 
the subject. It is only just to note, however, that the experimental 
work reported in this paper was planned and executed before Jo- 
hannsen reported his experiments. The experiment has now been 
revised to better fit the problem. 



ExPERIMENTAIv EvIDE;NCI5 

Believing that the practical experiments in tuber selection are 
of some value, we have made a study of the reported results. 

As early as i860 Hellriegel (55), from a three years' experi- 
ment, came to the conclusion that it is not possible to improve a 
variety of potatoes in starch content by the selection of tubers hav- 
ing a high specific gravity. His experiments gave the following 
starch contents from selections of tubers of high and low specific 
gravity : 



From mothers of liig"h specific gravity. 

«« " '« low 



1858 



1.0789 
1.0776 



1859 



1.0907 
1. 



1860 



1.0720 
1.0701 



It can be seen that the slight difference shown here might easily 
be due to experimental error and that there is no cumulative effect 
due to the selection. 

Franz (36) in 1878 concluded that from his experience and 
from general farm practice that varieties at least could be kept up 
in vigor by the selection of the seed. 

Emery (30) took a step in advance in method and used one 
hundred tubers from poorest hills as compared with one hundred 
tubers of the same weight from the best hills. His results were ir- 
regular and he came to no conclusion. 

Wollny (no) took a further step toward lessening experimen- 
tal error, and used only tubers of the same weight, but he concluded 
that selection of tubers with a high specific gravity shows no defi- 
nite influence upon the progeny either in quality or amount of yield. 

Later Marek (69) opposed these conclusions. His work is 
weak, however, from the fact that he divided his tubers into dif- 
ferent sizes, and after finding that the heaviest tubers were highest 
in specific gravity, he used them as seed. The results were probably 
due in great measure to the heavier seed piece used. 



404 



Bulletin No. 127. 



[August, 



Marek's work stimulated Wollny (113) to continue his inves- 
tigations. In this later work his former conclusions were modified. 
He found that in the majority of cases the progeny of tubers hav- 
ing a high specific gravity were of a slightly higher specific gravity 
than those descended from tubers of a low specific gravity. He be- 
lieves, however, that it is very doubtful whether any effectual im- 
provement of the value or yield of a variety could take place 
through selection of tubers of high specific gravity. Further in 
Marek's* final report, he admits practically the same thing. 

Girard (45, 46) reached the same conclusion with regard to 
specific gravity with the use of five varieties, but highly recommends 
the selection of high-yielding plants in the field as means of keeping 
up the yield of the variety. 

Hebert found no transmission of high specific gravity with a 
large number of experiments with Richter's Emperator. 

Wohltmann's (107) and Thiele's (96) results showed that the 
hereditary transmission of starch content had not been clearly 
proved. ^ 

Goff (49), in experiments begun in New York in 1884 and 
continued four seasons, found that the yield of tubers from pro- 
ductive hills was greater than that from unproductive hills, but that 
the difference in yield between different rows of selected tubers was 
often as great as the difference between the two selections, and 
even this might be entirely due to the fact that the plantings were 
all made from single eye pieces, which were larger in those from 
productive hills. Realizing the error in planting different weight 
seed pieces, he (50) began again in 1899. This time the same 
number of tubers and of cuttings were taken and the combined 
weights of each selection were made the same. The collected re- 
sults were as follows : 







Old long 


Mercer. 


Snowflake. 


Variety. 


Productive 
hills. 


Unproductive 
hills. 


Productive 
hills. 


Unproductive 
hills. 


Total No. of tubers 
produced in 2 yrs 


104 


68 


232 


195 


Total \vt. in oz. 

produced in 2 yrs 


64 


41 


332 


100 













*Marek, E., Deut. landw. Presse 1895:274. 



iQoS.] Improvement of the Potato. 405 

He concludes that the vig-or of the plant may be maintained and 
even increased by selection ; but that the experiment has not tended 
to increase the yield of the varieties used, for the reason, he says, 
of the continued cutting of the best tubers. 

Bolley (12) has for a number of years carried on an investiga- 
tion concerning the use of large and small tubers from the same 
hill. Bud end pieces of equal weight, cut to one eye piece were 
used, and all details of the experiment very accurately controlled. 
From three years' observations, he concludes that: "In planting 
equal weight pieces from small and large tubers of the same vine, 
there will not be a sufficient difference in favor of the one or the 
other size of potatoes to be noticeable under farm methods, pro- 
vided all are normally mature." This shows that selection of large 
potatoes from the bin will not necesssarily do anything toward im- 
proving the crop. He concludes also from his general observations 
on his stock, that variations in forms, size, roughness of skin, mal- 
formations, number of tubers, etc., are produced to some extent 
though influenced greatly by seasonal conditions. From this he 
concludes that selecting from high yielding plants should improve 
the yield. Later (13), he reports his first conclusions to be justified 
by more data. 

Fruwirth (43) criticises Bolley's work stating that he had 
found that large tubers were more likely to produce large tubers 
than were small tubers even from the same vine. He gives but 
few data warranting this conclusion, and I think that he overlooks 
Bolley's qualifying statement that "all must be normally mature." 

In 1899, Remy (85) saw a part of the error* in the work of 
former German and French chemists who used physical methods 
for determination of specific gravity, and estimated their starch 
from this by Maercker's tables. He found that a great number of 
the tubers had hollows in their centers which seriously vitiated his 
results. With the idea of correcting this fault, he selected good 
smooth potatoes weighing about 20og. each and used about yog. 
from the bud end for planting, while he determined the starch 
gravimetrically in the remainder by the use of Fehling's solution. 
The results for 1899 and 1900 show no definite relations between 
the nature of the seed tubers and the progeny either in dry matter 
or in starch content. This is the most exact experiment up to this 
time, although even^he chemical method for starch determination 
leaves much to be desired. The starch fluctuations were rather 
narrow, however, running in 1898 seed from 76.0 percent to 81.6 
percent calculated to the dry substance; and two crops are hardly 
sufficient to settle this question. 

From 1899 to 1901 appeared the notable contributions of 
Fischer (33, 34, 35) to this subject. He showed that there was 

*See writer's table of fluctuations in nitrogren content for further error. 



406 



Bulletin No. 127. 



[August. 



a definite relation between the shape of tubers, and starch content 
and power to yield, and that such individual characters were in a 
great measure transmitted. The author believed that he was war- 
ranted in (;pncluding that within a variety and under like conditions, 
fiat-round tubers produce those richest in starch, but weakest in 
yielding power, while cylindrical-oblong tubers give a progeny poor 
in starch content but of greater yield. The explanation of the cor- 
relation between starch content and fiat-round shape is from the 
following facts. The zone of highest content (see discussion con- 
cerning quality) in the potato lies next to the outside of the tuber. 
Other things being equal then, the tuber having the largest propor- 
tion of outer starch zone is the richest in starch. This is satisfied 
by the fiat-round tuber. 

In these investigations two varieties were used and selections 
made of rather small-fiat-round tubers on one hand, and large- 
cylindrical-long tubers on the other. The former showed a specific 
gravity of more than i.ii and the latter less than i.io. These 
specific gravities correspond in Maercker's tables to more than 20 
percent of starch in the former and less than 18 percent in the 
latter. 

The results were as follows : 



Variety. 


Group. 


Aver, weight 

seed tubers 

in grams. 


Yield in 

kilos 

per hectare. 


Yield kilos per 

ha. minus 

wt. of seed. 


Sachsische 


Flat- 
round, 
rich in 
starch. 


60.6 


21900 


19900 


Zwiebel 


Cylindrical 

long, 

poor in 

starch. 


68.0 


22600 


20360 


Reichs- 


Flat- 
round, 
rich in 
starch. 


47.4 


19900 


18340 


kanzler. 


Cylindrical- 
long, 
poor in 
starch. 


62 . S 


25305 


23290 



KJOS.] 



Improvement of the Potato. 



407 



In the year 1898 the expei"iinent was continued in order to see 
if a transmission of the relationships under discussion was contin- 
ued. For this reason both forms of tubers were selected from each 
group of the crop of 1897, giving in 1898 the following results: 



Variety. 


Form of tubers 

planted in 

1897. 


Form of tubers 

planted in 

1898. 


Aver. wt. 

of seed 
tuber in 

grams. 


Yield of 

tubers in 

kilos 

per ha. 


Yield of 
tubers in 

kilos 

per ha. 

minus wt. 

of seed. 


Sachsische 
Zwiebel 


Flat-round. 

Cylindrical- 
long. 


Flat- round 

Cyl.-long 

Flat-round 

Cyl.-long 


40.0 
89.5 
40.0 
70.0 


18500 
21730 
19840 
22080 


17180 
18780 
18520 
19700 


Reichs- 
kanzler. 


Flat-round. 

Cylindrical- 
long. 


Flat-round 

Cyl.-long 

Flat-round 

Cyl.-long 


43.0 
85.0 
43.0 
74.0 


22620 
25440 
24060 
27970 


21200 
22640 
22640 
25530 



An inspection of the table certainly appears to show an inherit- 
ance of yield in tubers which had been selected the year before, the 
most notable being the increase of yield in the Reichskanzler va- 
riety where the long tubers from the long tubers of 1897 show such 
a remarkable gain over the long tubers from the round tubers of 
1897, even though the seed weight of the latter is the greater. There 
are no final results on the starch content given. In his collected 
works (32) he states that a rise in starch content does follow se- 
lection of starch when determined by exact chemical methods. The 
author there concludes that the yield may be reduced by the con- 
tinued selection of flat-round tubers which are rich in starch, and 
increased by selection of cylindrical-long tubers, which would be 
poor in starch. 

Paulsen (79) makes a caustic criticism of Fischer's conclusions 
which may be summed up as follows : The form whether round or 
long is characteristic of the variety. According to Fischer's theory, 
a seedling plant showing round tubers should be rejected immedi- 
ately because they are less capable of improvement. Nevertheless, 
we have many round varieties which continue to give exceedingly 
high yields. 

In 1899 (40) and 1900 (41), Fruwirth reports that selection of 
tubers from high-yielding plants, as well as the choice of large 
tubers, afifects the yield, and recommends the selection as a practical 
thing especially to keep up the vigor of the variety. In 1903 (42) 
the same author reports that a change in the general characteristics 
of the plants of a variety follows only gradually when the variety 
is brought from an acclimated place to one witji a dififerent soil and 



408 



Bulletin No. 127. 



[August, 



climate. He argues that this in itself is a proof of hereditary trans- 
mission of a character acquired in the first place. Like results had 
been obtained already by Martinet (70). 

Hess (56) concludes that selection of vigorous mother plants 
which produce many tubers will bring about an improvement in 
the yield. His data do not warrant a definite statement. 

Briimer (14) in 1891 came to the same conclusions, but he ob- 
serves that the choosing of high-yielding plants only increases the 
yield when planted on a fertile soil. When planted on a poor soil, 
such a strain will set many tubers but they will be small. He ob- 
serves further that the use of vigorous, healthy plants as mother 
plants gives a noticeable protection from disease. A summary of 
his results is shown in the following table : 





Kind of 

mother 

plant. 


Experiment 1. 


Experiment 2. 


Variety. 


Wt. of 

seed 

tubers g. 


Yield 
kilos. 


Diseased 
tubers 
percent. 


Wt. of 

seed 

tubers g. 


Yield 
kilos. 


Diseased 

tubers 

percent. 


Mag-num 
bonum. . 


large 
small 


45-50 
45-50 


96 

77 


none 
none 


40-45 
40-45 


92 
65 


2 
3 


Schnee- 
flocke. . . 


large 
small 


35-40 
35-41 


55 
44 


6 
11 


35 40 
35-40 


61 

52 


8 
11 



In 1895 Sempolowski (91a) reported an investigation in which 
he selected his seed potatoes from mother plants producing at least 
fifteen tubers, and planted them in comparison with such ordinary 
stock as would usually be planted. His yield from the selected 
tubers was 25285 Kg. per hectare compared with 24555 Kg. per 
hectare from the ordinary seed. 

The experiments of Liebscher in which he came to negative 
results regarding hereditary transmission of tuber variations were 
continued at his death by von Seelhorst. The latter concluded in 
1897 that their experiments up to that time contained some grave 
errors, such as unequal depths of planting, non-uniformity of seed 
as to type and size, etc. These errors were his warrant for start- 
ing new experiments which he has reported in three notable papers 
(89, 90, 91). 

The experiments were with four varieties and I give below the 
collected results for the last year, 1903. The tubers used for seed 
are divided into two classes, large and small, which, as can be seen 
does away to a large extent with any influence due to differences in 
weight of the seed used. Determinations of starch in seed tubers 
and crop were also made and there was a notable transmission of 
starch to their proge/iy from high starch tubers. 



i908.] 



Improvement of the Potato. 



409 



Variety and 


Large seed tubers. 


Small seed tubers. 


kind of 
mother plant. 


No. 
tubers 
used. 


Aver, 
wt. g. 


Aver, 
wt. of. 
crop g. 


No. 

tubers 

used. 


Aver, 
wt. g. 


Aver, 
wt. of 
crop g. 


1. Phobus 

large yielding. . . 

small yielding. . . 


33 
15 


60.7 
51.7 


478 
301 


27 
18 


34.4 
30,1 


375 
206 


2. Frigga 
large yielding . . . 

small yielding.. . 


32 
12 


69.2 
51.8 


319 
113 3 


24 
14 


32.5 

27.7 


220 
80.9 


3. Viola 

large yielding. . . 

small yielding. . . 


25 
23 


65.3 
65.2 


372 
282 


22 
17 


36.6 

30.8 


314 

177 


4. Magnum bonum 
large yielding. . . 

small yielding. . . 


38 
2 


72.2 
87.0 


631 

500 


40 
10 


38.2 

35.2 


494 
603 



The exception in the case of Magnum bonum is explained by 
the fact that the seed of the crop from this variety was mixed in 
1899 ^^id the small potatoes used here may have been from large 
yielding vines before that. He concludes : "It is now without 
question to me, that we are able to raise the yield of potatoes by a 
not inconsiderable degree through the slight care in selection of 
seed, and also to prevent to a very great degree the degeneration 
of the newly improved variety." 

Later Martinet (71), Krzymowski (62), Eustace (31) and 
Parisot (78) have experimented along this line, but they have not 
generally carried on their investigations long enough to warrant 
definite conclusions. 

Summing up all evidence, it' appears that there are variations 
which may be transmitted in tuber propagation, but that in prac- 
tice a gain is rarely made by their selection. In general, results 
have been obscured by seasonal, climatic and local soil conditions 
which have a tremendous effect and which are not constant enouefh 
to permit tracing marked hereditary transmission. The changes 
that have been made in certain cases may be entirely due to muta- 
tions and not fluctuations ; or they may be due to the comparison 
of tubers that were physiologically different, such as diseased and 
healthy, or immature and mature tubers. Proper conclusions can be 
drawn only after controlled experiments upon an accurately meas- 
ured character by the use of biometrical methods. 



410 Bulletin No. 127. [Aui^hsI. 

m 

6. HYPOTHESIS OF DEGENERATION 
Analysis of the Question 

Very closely linked with the possible improvement of varieties 
by the selection of favorable fluctuations, and its equal in economic 
importance, is the alleged phenomenon of degeneration. The com- 
mon idea is, that there is a weakening, "a running out" of a variety, 
so that varieties within a greater or less number of years are cer- 
tain to become worthless for cultivation. That certain varieties in 
certain localities do lessen in vigor from year to year is not to be 
disputed. The question is are there contributing causes, or is it an 
inner physiological weakening, a protoplasmic degeneration, which 
must take place owing to long continued bud propagation. The 
proper analysis of the question is of great importance ; for, if such 
a degeneration must take place through obedience to physiological 
laws, our good varieties are necessarily doomed to a limited life. 
A proof that this is true, would make a great difference in the 
practicability of methods of tuber selection, where the improvement 
— if granted possible — would at least be slow. Methods of selec- 
tion to change the composition, involving expensive analyses of 
mother tubers, as in the case of sugar beets, would be absolutely 
prohibited unless the sexual transmission of these acquired char- 
acteristics could be shown. 

The common method of reasoning has been : Varieties have 
diminished in yield in certain places, and other varieties have been 
obtained. Nothing more is heard concerning the first varieties ; 
hence, it is concluded that they have declined, and, figuratively 
speaking, died. 

Hays (52) indicates the general belief in the following state- 
ment : 

"The age to whicl: a variety propagated by annually planting the root cut- 
tings of a single seminally produced plant will live before the necessity of 
renewal by sexual reproduction is not known. But since standard varieties of 
potatoes remain prominent for only about a third of a century there is some 
reason for the belief that the varieties reach their period of old age or senility 
in that time." 

The period of prominence of varieties is hardly a measure of the 
question, for hundreds of men are annually growing seedlings with 
which they hope to supplant current varieties and it would be re- 
markable if many old varieties were of sufficient merit successfully 
to hold their own. But nevertheless, even if the latter statement 
were not true, only a portion of the question is settled, Ehrenberg^ 



ig)cS.] Improvement of the Potato. 411 

(29) has lately discussed the question in all of its bearings from 
the practical standpoint, and divides it into three parts : ( i ) the 
aging (Altern) or senility of a variety, that is, a degeneration re- 
sulting from inner causes because of a prolonged and possibly un- 
natural propagation by means of tubers; (2) the deterioration 
(Ausarten) caused by a change to an unfavorable environment; 
(3) the loss of vigor due to lack of selection of the tubers (Herab- 
ziichtung). It seems that the last two might be united, for, set- 
ting aside the first question, it must be variation in outside influ- 
ences that causes sufficient variation in individual plants to make a 
basis for selection. We would then have the (juestions of variety 
senility, and of incomplete adaptation. 

The latter question is one of such common knowledge that it is 
hardly necessary to discuss its voluminous literature. It should be 
noted, however, that this has nothing to do with the question of the 
inheritance of partial fluctuations. 

In a letter written by Joseph Cooper (5), of New^ Jersey, in 
'1799, and published in volume one of the Memoirs of the Philadel- 
phia Society for promoting Agriculture, the matter seems to be gen- 
erally recognized. For fifty years, Cooper had maintained and 
improved without change, strains of pumpkins, early peas and as- 
paragus. "He made similarly successful experiments in keeping 
and improving strains of the potato for even at that time the com- 
plaint was 'very general,' as he writes, 'that potatoes of every kind 
degenerate.' " 

The id^a has changed little among farmers today, although 
some light has been thrown on the question. In 1876, Beal (8) 
reported an experiment in which a variety giving good yields de- 
generated in eight years so as to produce nothing, although other 
varieties were producing good crops on the same soil. Fruwirth 
(42) and Martinet (70) have explained this and the other numer- 
ous experiments of the same nature by showing that there is a 
gradual change of characters that takes place upon changing the 
locality, either for better or worse conditions. In other words, a 
variety coming from a locality favorable as to soil and climate 
to one unfavorable, is not able to adapt itself rapidly to con- 
ditions, as are seed propagated plants by means of their possibil- 
ities for greater numbers of combinations of characters. There- 
fore there is a final disclosing of the inadaptibility of the variety, 
although it takes place more or less slowly owing to the same law. 

It seems to the writer that the main economic question still un- 
solved is whether there is a gradual reduction of disease resisting^ 



4l2 Bulletin No. 127. * [August, 

power in varieties.* It has been commonly concluded from general 
observations by writers on potato culture that such is the case. 
There are varieties which in comparative tests with others, give 
small proportions of infected plants for a number of years and then 
show a notable increase in this proportion. This, however, may be 
easily explained. In plants propagated by seeds, when the vigor of 
any particular season's produce has been seriously impaired, the 
germinating power of the seed is likely to be affected and they are 
therefore either discarded for planting or fail to produce plants in 
the field, and the less vigorous strain perishes. With potatoes, an 
epidemic of any particular disease scarcely ever completely destroys 
the crop. The tubers weakened in vigor are planted the next sea- 
son ahd may possibly produce plants less able to withstand the ef- 
fects of futher infection. 

We have already seen the possibility of keeping up (not im- 
proving) varieties by selection, in the discussion concerning the 
transmission of tuber variations. Girard (45), who had probably 
a wider experience than any other investigator in the subject, — 
working as he did for eleven years with sometimes over six hun- 
dred co-operators, — sums up the whole matter as dependent on 
seed selection. However, the strict attention he paid to all matters 
concerning soil, fertilizers, planting and cultivation shows that he 
really laid great stress on favorable environment. He says : 

"It is an opinion quite broadly held that varieties of potatoes cultivated con- 
tinually in the same region, are certain to degenerate. It. is a frequent thing to 
hear large potato buyers or starch manufacturers declare that after having im- 
ported and placed at the disposal of their growers varieties of potatoes noted for 
their large crops, they have seen them give excellent results the first year, fall 
away the second year, and give results even lower than the native potatoes in 
the third year. This is indeed true but it is by no means inexplicable; the de- 
generation which one sees in this circumstance, does not result from a natural 
weakening of the variety; it simply results from the entire lack of care with 
which the plants to be perpetuated are chosen. All the good tubers are sold to 
the market, and it is from the inferior, discarded tubers that has been demanded 
a continuation of qualities which they cannot give. I have demonstrated prac- 
tically, and have established the fact that if suitable tubers are selected for 
planting and the cultivation accomplished with the needed care, the quality and 
quantity of the crop will be maintained under all satisfactory climatic conditions." 

Since such degeneration as is commonly noticed can be readily 
explained without resorting to any hypothesis of "variety senility," 
this division of the subject is still to be discussed. 

"It also may be that there is a natural selection of more virile strains of funtri. 



JQoS.] Improvement of the Potato. 413 

Biological Evide^nce 

It has long- been believed by a number of investigators that a 
conjunction of paternal and maternal nuclei is necessary for the 
"rejuvenescence of vigor" in the species. Life has been considered 
to be a cycle, running from conjugation to conjugation through a 
greater or less number of generations. This was considered by 
many to be definitely proved when ]\7taupas (72, 73) showed that 
colonies of Infusorians, when artifically prevented from conjugat- 
ing, invariably died out although often several hundred generations 
intervened. Later experiments along the same line by Galkins, 
however, have shown that a change in diet and the stimulus of a 
supply of chemical salts appear to be all that is necessary for con- 
tinued propagation of Infusorians without conjugation. An addi- 
tion of an extract of sheeps brains was all that was necessary to 
restore his colonies to full vigor after the 620th generation. ' 

The classical experiments of Tichomiroff and Loeb have shown 
that artificial parthenogenesis may be induced by both mechanical 
and chemical stimuli ; while Boveri and Delage have developed 
even non-nucleated ovum fragments to the larval stage. As one re- 
sult of these facts, we must conclude that fertilization produces two 
results : a. A combination of hereditary qualities ; b. A physiolog- 
ical stimulus to growth. But since other stimuli are found to pro- 
duce cell division, it is hardly reasonable that highly specialized 
sexual processes should have been developed with the second result 
as their primary, objects. Indeed Weismann (105 v. i p. 343) has 
concluded that the sole immediate effect of conjugation is "the com- 
bination of the hereditary tendencies of two individuals into one." 

It appears that we have no data among wild plants from which 
we are compelled to conclude that continuous bud propagation is 
opposed to any natural law. Vines* writing of the Basidiomycetes 
says "These fungi are not only entirely asexual but it would appear 
that they have been evolved in a purely asexual manner from asex- 
ual ascomycetous or aecidiomycetous ancestors. The basidiomycetes, 
in fact, afford an example of a vast family of plants of the most 
varied forms and habits, including hundreds of genera and species, 
in which, so far as minute and long continued investigations have 
shown, there is not and probably never has been, any trace of a sex- 
ual process." 

Late cytological investigations have shown sexual processes, or 
at least nuclear fusions similar to those of the higher plants and 

*ViQes, Nature 11: p. 625, quoted by Reid: Principles of Heredity. 



414 Bulletin No. 127. [.In^usr, 

m 

animals, in some of these fungi ; but there are other species, and 
among animals, some species of crustaceans, which reproduce ex- 
clusively by parthenogenesis. Some of the fungi are thought to 
have vestiges of degenerate sexual organs, and in the Crustaceans 
it can be demonstrated (105) that they once reproduced sexually, 
by their possession of the sac which once served for receiving 
the spermatozoa. It is extremely improbable that a process neces- 
sary or even advantageous to the continuance of any species could 
ha\'e been allowed to degenerate under the operation of natural se- 
lection. 

In higher plants we have numerous examples where either no 
seed is produced or where seed propagation is seldom resorted to 
and yet we hear no serious charges of degeneration. Among them 
may be given the banana, hops, strawberry, sugar cane and many 
of the grasses. There are also certain parthenogenetic plants, such 
as the dandelion, that are certainly in no danger of dying out from 
their method of seed production. 

The fact of degeneration in potatoes seems to have been ex- 
plained as variety senility due to bud propagation, as a convenient 
prop to various hypotheses as to the function of sex; and this con- 
clusion on theoretical grounds is decidedly unproved. 

Experimental Evidence 

So far as I am able to learn the senility theory was first pro- 
pounded about 1806 by Knight (61) although he did not lay special 
stress on potatoes. His hypothesis was that all varieties propagated 
by buds (particularly fruits) have a most productive period when 
they are of middle age and then become "subject at no very distant 
period to the debilities and diseases of old age." 

Aitken (i) first applied the hypothesis to potatoes in 1837. 
He believed that although most fruits were produced from seed 
each year, a potato variety was a single plant propagated yearly 
through its tubers, and must grow old in the process. The first 
sign of this weakening of the variety, he says, is a lack of blossoms. 

In Germany, Berchtold (9) in 1842 accepted Aitken's view with 
limitations. He considered that disease, climate, soil, cultivation 
and other conditions were the important factors to be considered. 

Later Heine (53) of Emersleben, who was for ten years the 
chief German writer on potatoes, was very pronounced in his ac- 
ceptance of Aitken's theory, and was followed by many of his 
countrymen. He speaks continually of "the unalterable law of na- 
ture that only through sexual seed propagation is it possible to 



iQoS.] Improvement op" the Potato. '._ 

keep potato varieties lastingly high in yield." It is exceedingly in- 
teresting to note, however, that VVestermaeier (io6) who suc- 
ceeded Heine in his work has finally come to the conclusions that 
in Heine's results the contributing factors were not differentiated 
from the real cjuestion, and that it seems to him that it is question- 
able whether there is any such thing as variety senility. 

The later conformers to Heine's views are Paulsen (43), Cim- 
Ijal and Marek. 

The first weighty objection to this theory was made by Julius 
Kiihn (64) in 1871. He says: "The theory of a degeneration of 
the potato is disproved as untenable" and continued for several 
years thereafter to combat Aitken's theory. Busch (15) continued 
the opposition and seems to be really the first to recognize the true 
question. He says : "A degeneration in the sense of an increasing 
deterioration through the w^eakness of old age, does not exist." 
His views were endorsed and enlarged upon by Wollny (108), 
Liebscher (66), Girard (45), Thiele (96) and Fischer (33) who 
jiave all considered the question apart from that of degeneration 
through lack of adaptation to environment. 

Ehrenberg (29) in 1904 makes a complete survey of data of 
Heine, of the deutschen Kartoffelkulturstation, and of Paulsen, the 
first and last of these running from 1877 to 1903. He discusses all 
the contributing sources of error and comes to the conclusion that 
"Ein Altern der Kartoffel gibt as aller Wahrscheinlichkeit niclit." 
And indeed, it appears that the people who have considered this 
single cjuestion are unanimous in opposition to the hypothesis of 
variety senility. The English and American writers do not seem 
to have considered the questions apart, although Bailey (5 p. 380) 
and probably others have recognized the division. He says : 

"The presumption is that varieties propagated by buds wear out sooner 
than those propagated by seeds, for the experiments of Darwin and others have 
shown that the special office of seed propagation is to increase the virility of the 
species through cross fertilization. It must follow therefore, that in the ab- 
sence of cross fertilization virility must be less. 

"But we do not need to consider this phase of the question, for we are 
concerned with variation (that is, running out) rather than with ultimate 
longevity (or wearing out). Further, it is also probable that any tendency 
toward weakness through lack of fertilization is fully counterbalanced by the 
protection which such varieties receive under cultivation." 

The work of the U. S. Agricultural Experiment Stations bear- 
ing the nearest relation to this question are those experiments deal- 
ing with cormparative value of home grown and northern seed 
tubers. There is a wide spread belief both in this country and in 



416 Bulletin No. 127. * [August, 

England that northern grown seed is the superior, and should be 
obtained every two years or so because of degeneration. It is 
interesting to note that in experiments at six stations* in the early 
nineties, all show results slightly in favor of home grown varieties. 
It is probable that in these experiments more care was paid to seed, 
fertilizers and cultivation than is usual to growers, resulting well 
for home grown seed; nevertheless, had the results been different, it 
would only have shown, either that the northern grown were better 
adapted to such climate or the soils there found, or that in coming 
from growers who made a commercial business of supplying seed 
tubers, they had been given better care in regard to selection and 
environmental conditions. 

Relying for our conclusions on the philosophical grounds and 
the practical work of the German and French investigators, it seems 
tenable that there is no variety senility and that we are warranted 
in excluding this from our calculations as to commercial methods 
of producing varieties adapted to certain conditions. The more 
serious practical question, is the manner in which outside pernicious 
influences are to be avoided. As methods of cultivation and seed 
selection are pretty well established and soil, plant food and climatic 
conditions can be determined and partially controlled in each local- 
ity, it seems to the writer that here again the matter of disease con- 
trol is the thing of primary importance. It is questionable, with- 
out disease resistance or comparatively certain disease control, if 
expensive work should be done to improve varieties in particular 
characters such as starch content, by selection of seedlings on the 
basis of a chemical analysis. For it is reasonably certain that we 
could not expect this improvement to be transmitted, if we were 
forced by loss of vigor due to disease attacks to return to sexual 
propagation. The latter, however, is a matter which we can say is 
yet unproved. 



*IlUnois, Vermont, Maryland, Georg-ia, Louisiana, and Missouri. 



1908.] Improvement of the Potato. 417 

7. DISCONTINUOUS VARIATIONS 
Mutations 

It has long been recognized that in potato varieties there some- 
times appear marked bud variations which when propagated are 
true to type. If we accept DeVries' idea of mutations, and if we 
beHeve that bud mutations are of practically the same nature as seed 
mutation ; then they may be either progressive, degressive or retro- 
gressive. Such variations which have been noticed have always 
been relatively wide ones, but it is not inconsistent with the theory 
to have mutations which are within the limit of fluctuating varia- 
tions. As the writer understands the question, these mutations may 
be either bud-mutations, which may not be propagated by seed ; or 
mutations affecting the gametic structure, which will always be in- 
herited unless new mutations intervene. 

Darwin (21) mentions three cases, one in which a single white 
eye in the purple variety Forty fold, became the "parent" of a white 
variety. In another case this same variety produced a whole white 
tuber which bred true. The third case was that of the white Kemp 
potato which produced a red spot which was propagated and 
yielded a variety of much prominence, which was called Taylor's 
Forty-fold. In the United States there has been a number of vari- 
eties on the market for several years which have originated in this 
way. Among them are Thorburn's Late Rose, the White Victor and 
White Early Ohio. I should roughly estimate that less than 0.5 
percent of our present varieties are from bud-mutation. The gen- 
eral belief is that these variations are confined to tuber color or pos- 
sibly to tuber color and shape. Wohltmann (43) has offered an ex- 
ception; a variation in flower color in the Leo variety although it 
was unknown whether the variety came from one or several seed- 
lings. It certainly seems that the variations are almost always con- 
fined to the tubers, but this should be expected as the tubers are the 
modified part. The probability is that color is the only character 
that is easily gauged, and that if accurate methods of estimating 
other characters were used, they too would be found to vary. The 
supposed rarity of these occurrences has made them of little com- 
mercial importance, but it is very possible that with strict search, 
they might be shown to occur much oftener than is expected. 

As stated before, data which I have collected appear to show 
that bud-mutations are usually — and possibly always — the loss of 
the dominant character of an allelomorphic pair, with the conse- 
quent appearance of the recessive character. This data will be pub- 
lished in a separate paper. 



^ 



418 Bulletin No. 127. * [August, 

8. GRAFT-HYBRIDS 

We have in graft-hybrids another method in which there may be 
a possibiHty of an improvement of the potato. 

There is still a great deal of argument as to the authenticity of 
graft-hybrids which have been reported. The negative reasoning 
being chiefly theoretical, owing to their present inexplicability. 

Darwin (21) collected a large number of cases where asexual 
hybrids of the potato seem to have been made. He himself was 
fully convinced as to their authenticity although he recognized the 
fact that the scoffer might attribute them to bud variation induced 
by the graft. He argues that the variation was always between the 
parent forms. 

Daniel (19, 20) who has made by far the most extended study 
of grafts, says that, "While formerly it. was considered that grafted 
scions lost none of their own characteristics and acquired no new 
ones from the stocks on which they were grafted, recent work 
indicates that this view must be modified." He states that hybrid- 
grafts can be fixed and propagated; and mentions the Edouard Le- 
fort potato produced by vine graft of Majolin and Imperator and 
partaking of the character of each. He believes, however, that 
asexual hybridization is neither constant, regular nor very frequent. 

Bift'en (11) grafted tubers with different characters, and while 
convinced of the authenticity of the phenomenon, he states that 
"Tubers in which two types are blended, never occur." In halving 
the tubers transverely, each portion was indistinguishable from one 
of its parents. Each half of the tuber showed all the characters of 
one parent and not certain dominant ones. The graft-hybrid was in 
this respect different from the seed hybrid. 

There is at present no cytological explanation of such a phe- 
nomenon, but from the apparent ease with which hybrid-grafts are 
made, or at least by which bud variations are caused through such 
stimulus, this seems to be a very interesting field for investigation. 
If in potato improvement we could in time learn to make a reason- 
able percentage of successful hybrids and the characters would blend, 
it might settle the quandary in which we are at present, in trying to 
get crosses with many of the excellent varieties which produce little 
or no viable pollen. On the other hand, if it finally proves that 
there is not a true hybrid formed, this method may still prove valu- 
able as a means of obtaining bud-mutations. 



iijoS.] Improvement of the Potato. 419 

9. QUALITY 
Historical 

In 1897 Coudon and Boussard (18) came to the conclusion on 
the ground of their tests with thirty-four varieties of potatoes that 
their cidinary vahie is dependent upon the chemical composition, 
and that it varies directly as the nitrogen content and inversely 
as the starch content, that is culinary value = "Itl^ch" ' Potatoes 
with a high starch content were disintegrated by boiling, and pota- 
toes with a high nitrogen content resistant. 

Their analyses were made of four physical divisions of the po- 
tato as shown in figures. These parts they designated, from out- 
side to inside, as skin, cortical layer, outer medullary layer and in- 
ner medullary. 



/ , 




; 



Fig. 5. Zones of the Potato. (After Coudon and Boussard.) 

a. Cortical layer. 

b. External medullary layer. 

c. Internal medullary layer. 

The outer skin is the colored portion and may be completely 
separated from the part underneath. The cortical or fibro-vascular 
layer lies next and is easily distinguished by the separating line of 
vascular bundles. In the interior the inner medullary layer appears 



420 



Bulletin No. 127. 



[August 



like an undeveloped stem branching out toward the eyes. The re- 
sults of their analyses of these parts, calculated to the fresh basis 
are: 

Composition of the Different Zones of the Potato Tuber 



Variety. 


Zone. 


Water. 


Starch. 


Total 

nitrogenous 

matter.* 


Bleue 
geante. 


Cortical 

Out. med 

In. med 


72.74 
74.33 
81.72 


21.14 
19.78 
12.30 


1 91 
1.88 
2.14 


Czarine. 


Cortical 

Out. med 

In. med 


72.92 

78.87 
84.48 


22.45 
15.64 
10.50 


1.84 
2.17 
2.17 


Saucisse. 


Cortical+ 
Epidermis .... 

Out. med 

In. med 


78.72 
79.12 
80.73 


14.38 
13.47 
12.31 


2.22 
2.39 
2.62 



I 



The water and nitrogen contents increase as we go from the 
outer to the inner zones, while the starch content decreases. It is 
also interesting that the percent of proteid nitrogen to the total ni- 
trogen decreases in the inner zones; the former being 68.7 percent 
in the cortical layer, 56.0 percent in the outer medullary layer and 
47.3 percent in the inner medullary layer. 

This work was believed to give a chemical basis for the selection 
for planting, of tubers which were of better table quality. It should 
be noted, however, that the standard for table quality in France is 
decidedly different from that in the United States. The accepted 
method of cooking there is frying in deep fat, for which a potato 
which holds its form is desired ; while in this country probably nine- 
tenths of the consumption is of boiled potatoes, which are desired 
dry and mealy. Potatoes imported from Vilmorin, which I have 
examinefl. ne^rlv all possessed a yellow flesh, a strong flavor, and 
were firm and soggy after boiling. 

Shortly after the appearance of this work, Frisby and Bryant 
(38) reported separations and analyses of these different zones in 
the American variety "White Star," without separating the outer 
and inner medullary layers, and found the following composition : 

Zone 

Cortical layer 

Outer and inner Med 



Water perssnt 


Proteid N. 


Total N. 


IT. free extract 


83.2 


.24 


.36 


12.6 


81.I 


.18 


•32 


15-7 



♦Probably total Nx().25 althoug-h it i.s not stated. 



I908.] 



Improvement of the Potato. 



421 



These results are in direct opposition to Condon's and Bous- 
sard's as to nitrogen and starch but the discrepancy may have been 
due to the different methods of determination. Nitrogen free ex- 
tract gives total carbohydrates minus crude fibre, at all times, while 
a direct starch determination is very different when made in the 
fall from one made in the spring when large quantities of starch 
have been changed to sugar. 

In 1901 Waterstradt and Willner (104) reported extended 
investigations on the same subject. Their results are more appli- 
cable to American conditions for the reason of similarity of stand- 
ard of quality in Germany and America. Nine varieties were used, 
each of which was grown on two separate fields. Of these varie- 
ties, three were recognized to be of good table quality, three were 
coarse starch producing varieties and three were on the border line 
between the two. I give here the average composition only of the 
first and second classes : 



Place 
grown. 


Class. 


Zone. 


Fresh basis. 


Dry basis. 








Dry 
mat. 


Tot. N. 


Starch. 


Dry 
mat. 


Tot. N. 


Starch. 


Berlin 
Exp. 
Field. 


Eating- 
var. 


Cor 

Med.. . 


24.3 
19,8 


0.336 
0.363 


18.17 
14.74 


100. 
100. 


1.34 

1 85 


75.03 
74.50 


Coarse 

starch 

var. 


Cor 

Med. .. 


26.9 
23.1 


0.359 
0.355 


20.61 
17.76 


100. 
100. 


1 34 

1 55 


75.68 
76.87 


Marien 


Eating- 
var. 


Cor.... 
Med. . 


27.3 
24.1 


0.365 
0.391 




100. 
100. 


1.35 
1.56 





Field. 


Coarse 

starch 

var. 


Cor 

Med. .. 


30.6 

27.3 


0.354 
0.383 




100. 
100. 


1.17 

1.42 





This table shows that potatoes of better table quality are 
markedly lower in starch than the others, as was to be expected 
from the German classification. The dry matter in the cortical 
layer is regularly higher than in the medullary layers, as is the 
starch content when calculated to the fresh basis. When calculated 
to the water free basis, however, the starch variations are slight. 
The total nitrogen variations corroborated the results of Coudon 
and Boussard. 



422 



Bulletin No. 127. 



[August. 



In order to find the proportion of cortical layer and inner medul- 
lary layers, the authors cut the potatoes in half through the long 
diameter, marked the line of demarcation of the two layers on 
paper and weighed the corresponding slips.* The average of all of 
the good eating varieties in proportion of cortical layer to inner 
medullary layers was 100:121.5, while the proportion in the coarse 
varieties was 100:140.4. The actual cooking tests bore out their 
opinion of the relative cooking value of the varieties as expressed 
in their classification, and they concluded that chemical composition 
could not be used as a basis of selection for cooking value. 

In 1905 Gilmore (44) published an excellent paper in which he 
tentatively concluded that the culinary value of the potato depended 
not so much upon its chemical composition as upon its anatomical 
and perhaps its physiological structure. 

Experimental 
Composition of Different Parts 

The first object in this work was to see if American varieties 
and especially if within a variety, the table quality is dependent 
upon the total nitrogen content. 

The two varieties Rural New Yorker No. 2 and Carman No. 3 
were selected as being representative popular varieties. Careful 
mechanical separations of the different zones were made in five in- 
dividual potatoes of each variety, after the manner of Condon and 
Boussard. Dry matter was determined at 104 degrees C in a cur- 
rent of hydrogen, and total nitrogen was determined by the regular 
Kjeldahl method, as were all similar determinations here reported. 
The averages of the results of each variety are shown in the fol- 
lowing table : 

Table 3. Composition of Parts of the Potato 



Variety. 


Zone. 


Dry matter, 
percent. 


Tot. N. 
fr. bas., 
percent. 


Tot. N. 
dr3' bas., 
percent. 


Rural 
N. Y. 

No. 2. 


Cortical 

Outer med .... 
Inner med 


20.95 
18.46 
14.04 


0.46 
0.47 
0.45 


2.20 
2.56 
3.23 


Carman 
No. 3. 


Cortical 

Outer med. . . . 
Inner med .... 


22.20 
19.41 
14.92 


0.49 
0.51 
0.52 


2.23 
2.63 
3.49 



♦This method does not show the correct relation. If tlie potatoes were considered as sper- 
jcal, the relation would be (whole dianieter)'-(tne^ullary diameter)^: (medullary diameter''). 



IQOS.] 



Improvement of the Potato. 



423 



The content of dry matter is quite variable and regularly de- 
creases from the outside to the inside of the three zones. The 
total nitrogen content is only slightly variable in the three zones, 
though showing a regular increase to the inner medullary layer, 
when calculated to the dry basis, owing to the variability of the 
water content. Ash determinations made on ten samples varied little 
from 0.90 percent on the fresh basis, showing that carbohydrates, 
estimated by difference, are higher in the cortical layer, and quite 
low in the inner medullary layer. From this we may conclude that 
there is a difference in time of cooking in the different zones of the 
potato, and that the glistening appearance of the cortical layer after 
boiling would be accounted for by its larger starch content breaking 
open the cell walls. 



Sampling 

Since there is such a dift'erence in the composition of these dif- 
ferent zones, it is extremely difficult to obtain a correct sample of 
the tubers for analyses without spoiling them for cooking tests or 
for planting. A number of methods were tried, the one giving the 
most satisfactory results being that of a cylinder cut with a twelve 
mm. cork borer, parallel to the long diameter, but a little to the 
side. This takes in only a portion of the inner medullary layer and 
compares well with the composition of the whole potato. The 
greatest difference in five determinations of total nitrogen on indi- 
vidual tubers was 0.04 percent calculated to the fresh basis. 

Table 4. Variations in Sampling 



Potato No. 


Total N. per cent 
in cylinder. 


Total N. 
in whole tubers. 


1 
2 
3 
4 

5 


0.37 
0.43 
0.49 
0.42 
0.46 


0.34 
0.41 
0.50 
0.43 
0.44 



This method has been used in all subsequent determinations 
when tubers were to be used for cooking tests for planting. 

Relations of Total Nitrogen Content and Quality 

To ascertain the relation of total nitrogen content to quality, a 
number of tubers of the Rural New Yorker No. 2 variety in which 



424 



Bulletin No. 127. 



[August, 



total nitrogen and dry matter had been determined, were tested by- 
boiling. Corks were tied in the holes, whence the sample for analy- 
sis had been taken. City water from artesian wells, containing a 
considerable amount of salts, was used, but no sodium chlorid was 
added. On account of the amount of work necessary to secure 
samples with a sufficient variation in nitrogen content, only ten of 
each kind were used. So small a number makes the probable error 
large, especially as no method of judging the quality has been de- 
vised except an arbitrary personal judgment. The flavor and the 
table quality aside from flavor were judged, dividing the array into 
five different classes.* 

Their selection for high nitrogen content did not seem to affect 
the average of the two classes in weight or dry matter to any consid- 
erable extent, as is shown below : 



Averages : 



Table 5. Quality of High Nitrogen Potatoes 
Wt. 2o6g. Percent Dry matter 21.09. Percent N. Dry basis 2.27 



Potatoes 
used. 


Average 
total N. 
content. 


Quality and appearance. 


Flavor. 


g-ood. 


fair. 


med. 


poor. 


very p. 


good. 


fair. 


med. 


poor. 


very p. 


10 


0.48 


1 


5 


2 


1 


1 





3 


5 


2 






Table 6. Quality of Low Nitrogen Potatoes 
Averages : Wt. 2i8g. Percent Dry matter 21.99. Percent N. Dry basis 1.62 



Potatoes 
used. 


Averaee 
total N. 
content. 


Quality and appearance. 


Flavor 


good. 


fair. 


med. 


poor. 


very p. 


good. 


fair. 


med. 


poor. 


very p. 


10 


0.36 


1 


4 


2 


2 


1 


1 


3 


4 


2 






The tables indicate that variation in nitrogen content does not 
have a noticeable effect on quality, although there is a slight indi- 
cation that extremely high nitrogen might make the flavor more 
pronounced. High nitrogen potatoes can therefore be propagated 
without correlation adverse to quality, weight or dry matter. 

*It should be noticed that in these tests by arbitrary standard only the results of any one 
experiment should be compared with each other, for it is impossible to keep in mind an arbi- 
trary standard from week to week to compare separate tests. The tubers in every case were 
known by numbers only. 



I908.] 



Improvement of the Potato. 



425 



Rei<ations of Dry Matter and Quality 

In the same manner as above, selections of potatoes of different 
dry matter content were tested. As far as was possible tubers of 
relatively the same weight were used, in order to have the same time 
of cooking. Otherwise the selection was entirely by dry matter: " 

Table 7. Quality as Related to Dry Matter 



Potatoes 
used. 


Dry 
matter. 


Average 
total N. 
fresh b. 


Average 
wt. 


Quality other than 
flavor. 


Flavor. 


S- 


f. 


m. 


P- 


V. p. 


g- 



f. 



m. 



P- 

2 


v. p. 


8 


16-17% 
Aver. 
16.50 


0.40 


219 








1 


3 


4 


6 


10 


17-18% 
Aver. 
17.56 


0.42 


232 





2 


3 


3 


2 








1 


6 


3 


10 


19-20% 
Aver. 
19.62 


0.45 


228 


2 


4 


4 








1 


3 


4 


2 





10 


21-22% 
Aver. 
21.65 


0.44 


204 


1 


4 


3 


2 





1 


5 


4 








10 


23-24% 
Aver. 
23.44 


0.44 


220 

1 


2 


4 


4 








1 


4 


5 








8 


25-28% 
Aver. 
26.09 


0.38 


208 


1 


3 


3 


1 





2 


3 


3 









This table shows that there is a lower limit in amount of dry 
matter or more probably of carbohydrates, below which tubers can- 
not be of good quality. In this variety it is about 18 percent dry 
matter or probably about 15 percent starch. 

When the dry matter is above this lower limit, the quality does 
not seem to be directly affected. It may be that this lower limit is 
different in different varieties, and that owing to the general low 
dry matter of these samples the standard of quality was put too low. 
However some excellent potatoes were found with a total dry mat- 
ter as low as 19 percent. 

Waterstradt and Willner showed that in certain German varie- 
ties those tubers with very high starch content were of coarse qual- 



426 



Bulletin No. 127. 



[August, 



ity. We found no potatoes nearly up to this limit, but from general 
experience we should conclude that potatoes with a starch content 
above a certain limit would easily fall to pieces, or if the cell walls 
were strong enough to hold together under such pressure, they must 
necessarily be coarse and woody. 

Physical Structure and Quality 

The writer was led first by Condon's and Boussard's work to 
believe that the physical structure held some relation to the table 
quality. Microscopical examination of the structure of the potato 
bears out the chemical analyses of the different zones. 




Fig. 6. a. Outer section of cortical layer, b. Inner section of cortical 

LAYER. 

(Figures 6 and 7 from the same tuber.) 

The cortical layer (figure 6), below the first few layers of 
cells which are removed with the skin, shows a remarkably larger 
amount of starch in the cells, than does the internal medullary layer 
(figure 7). The starch content of the external medullary layer is 
also greater than that of the internal. The grains of starch in the 
cortical and external medullary layers besides existing in greater 
numbers per cell, are generally of larger average size. The paucity 
of starch in the internal medullary layer causes the cells to be only 
partially filled with the cooked starch and the cell walls are scarcely 
ever ruptured. In the cortical layer, on the other hand, the amount 
of starch is such that in the swelling due to cooking, the cells 
are filled completely and many of them ruptured, causing the mealy 
appearance so much desired by the consumer. 



ipoS. 



Improvement of the Potato. 



427 





Fig. 7. a. Section near the vascular bundles showing portion of external 

MEDULLARY LAYER, b. SECTION OF INTERAL MEDULLARY LAYER. 

It is quite evident then that potatoes having as far as possible 
a homogeneous flesh and containing as large an amount as possible 
of cortical and outer medullary layers in proportion to inner medul- 
lary layer, should be of the finest quality. 

This has been shown to be a fact in experiments with fifteen 
American varieties even though cooked after having been split* in 
half, which is manifestly a disadvantage. 





Fig. 8. Cross sections of potato of good quality. Large cortical and exter- 
nal MEDULLARY LAYERS^ AND SMALL OR FINELY DIVIDED INTERNAL MEDULLARY 
LAYER. 



*In a number of these tests the halves of the potatoes were fastened together again before 
cooking-, in order to make the test as near as possible like ordinary practice. The judg-ment 
of the quality was made by two different persons. The tubers were known only bv number, 



428 Bulletin No. 127. [August. 

Table 8. Physical Selection of Potatoes for Table Quality 



Variety. 


Selected physically 
for quality. 


No. tubers 
used. 


No. tubers 
good qual. 


No. tubers 
tned. qual. 


No. tubers 
poor qual. 


B. Six Weeks 


g-ood 
poor 


10 
10 


8 
1 


2 
3 



6 


E. Ohio 


good 
poor 


10 
10 


10 

2 



3 




5 


Houlton Rose 


good 
poor 


10 
10 


9 



1 
2 



8 


Irish Cobbler 


good 
poor 


10 
10 


10 

3 




2 




5 


Minister 


g-ood 
poor 


10 
10 


7 
2 


3 

3 







5 


Carman No. 3 


good 
poor 


20 
20 


16 
4 


3 

5 


1 
11 


Rural N. Y. No. 2... 


good 
poor 


20 
20 


16 

5 


4 
5 



10 


Green Mountain 


good 
poor 


20 
20 


16 

3 


2 

7 


2 
10 


State of Maine 


good 
poor 


10 
10 


12 

2 


8 
10 




8 


Gem of Aroostock. . . 


good 
poor 


10 
10 


8 



10 
10 


2 
10 



From fifty to one hundred tubers were used in making- each of 
these selections, all of which were grown on the same type of soil, 
(a light sandy loam), in a single acre plot. In making selections it 
was very noticeable that there was a great varietal difference in 
quality. As the table shows, in some varieties it was very easy to se- 
lect tubers of good cooking quality, while in other varieties no sharp 
distinctions could be made. In Rust Proof, Ionia seedling. Twen- 
tieth Century, Gold Coin and Early Manistee no potato of good 
quality could be found although there were a number classed as 
medium. This is perhaps due to the fact that this was the first year 
any of the stock had been grown in Connecticut and they may not 
I'ave been adapted to the particular kind of soil on which they were 
crown. I have learned that all of these varieties except Rust Proof 
sometimes are of fair quality in other places. 

It seems evident from Table 8, that this anatomical difference 
is a varietal character, the difference between varieties being very 
great. The difference in quality within the variety, however, with 
as similar environmental conditions as it was possible to give, is 
almost as great as the difference between varieties. 



IQOS.] 



Improvement of the Potato. 



429 



Unfortunately this method cannot be used in selecting potatoes 
for the table, on account of the necessity of their cutting. Whether 
the extreme variations toward homogeneous structure are correl- 
ated with quality to a sufficient degree to be used as a means of im- 
proving varieties in quality; or whether fluctuations due to slight 
environmental differences impossible to control, obscure the herit- 
able variations, is now being investigated. There still remains the 
Dossible explanation that the other factors influencing quality are 
the causes of the great varietal differences, although our work in- 
dicates that this is not probable. We hope that it will be possible 
to use the method in determining the rejection of seedlings after 
a cross. The tubers from the different first year plants should be 
kept in different bags and at planting time selections made of those 
tubers having a large cortical layer and a small internal medullary 
layer branched in fine divisions, — the idea being to have the in- 
ternal structure of the potato as homogeneous as possible. 





Fig. 9. Cross sections of potato of poor quality. Small cortical layer and 

LARGE thick INTERNAL MEDULLARY LAYER. 



Other Factors Influencing Quality 

I. Color of skin. — Potatoes from seedlings of a single cross 
varying in color of skin to white, light brown, pink and red did not 
show any greater variation in quality than did those of a single 
color. Hence it may be concluded that color is not correlated with 



430 Bulletin No. 127. • [Ausiist. 

quality. Wc found varieties of all colors except the purple types 
which were ot good quality. No purple skinned potatoes were 
available which were of a size that indicated maturity and this 
might account for the fact that they were of a poorer quality. 

2. Nature of skin. — Those varieties which have a netted skin 
were found to be generally smooth-skinned when immature. A 
corky appearance indicated both maturity and a better keeping 
quality. In some cases one end of the tuber had a corky netted skin 
while the other end was smooth; these were generally different in 
internal structure, indicating some obstruction to perfect develop- 
ment. Very rough-skinned varieties as Russet and Scabproof were 
in general less susceptible to infection with potato scab, but were 
neither of better quality nor of higher starch content than other 
varieties grown under the same conditions ; which is in opposition 
to the conclusions of Krzymowski (63). 

Lenticels were found to be present in all sizes of potatoes and 
were well developed in individuals of most varieties. A develop- 
ment of strong healthy lenticels indicates maturity in the tuber al- 
though a number of writers have pointed out that possibly scab in- 
oculation takes place in them. 

3. Color of flesh. — White fleshed tubers are the only ones at 
present accepted in the American markets and it may be that yel- 
low^ flesh is correlated with a strong flavor and a poor quality 
by our standard. A number of varieties with a yellow flesh im- 
ported from France and considered by the French to be of prime 
quality were tested and were gummy and hard after boiling. 
These varieties are considered of good quality for frying and for 
use in salads. 

4. Shape. — Round potatoes as Noroton Beauty, and oblong 
round potatoes as Early Ohio have both been found to be of excel- 
lent tal)le quality, but the general popularity and prime quality of 
the round flat (as Irish Cobbler) and short-oval-flat types (as in 
Carman's productions), seem to support Fischer's view that po- 
tatoes of these types are better. The greater possible percentage 
of cortical layer in these types seems to be sufiicient reason for the 
conclusion, but there is a further argument in the fact that salad 
potatoes are usually small round types, or long slender types as the 
Lady Finger. 

5. Depth and frequency of eyes. — Great depth of eyes will be 
avoided because of the waste in peeling. A number of writers 
have also stated that extremely deep eyes tend toward coarseness 
of the variety, and indeed this seems to be the case. The vital- 



11>0S.] ImI'KUVEMENT UK THE PuTATO. 431 

ity of the sprout produced varies directly as the size and depth 
of the eyes, which is worthy of note in selection, otherwise types 
might be bred with eyes too shallow. 

The number of eyes has a marked effect on the quality, due to 
the fact that the internal medullary extends a branch to each eye. 
This makes the quality, other things being equal, vary inversely 
with the number of eyes. This variation within the variety is 
very great, varying in a count of 219 tubers of Rural New Yorker 
No. 2 from 7 to 28. 

In 1902, in the course of this work, 189 tubers of the variety 
Rural New Yorker No. 2 had been analyzed and a large number 
having been cooked were found to be of very good quality al- 
though the average dry matter content was only 20.74 percent. 
The modes for eyes in this lot was 12. 

Table 9. Variations in Number of Eyes in Rural New Yorker No. 2, 1902 





No. of eyes 
Frequencies 


7 8 9 10 
3 4 9 15 


11 
21 


12 

32 


13 
15 


14 
20 


IS 
13 


16 
19 


17 

12 


18 

13 


19 

6 


20 

4 


21 

2 


22 
1 



In 1903, 219 tubers of the Early Ohio variety were used, and 
were found to be of much poorer quality than those used in 1902, 
though of similar size and of pleasing appearance. The average 
dry matter content was only 16.15 percent or 4.59 percent lower 
than the others. The mode for the number of eyes was here 15 
as compared to 12 in the better variety. 

Table 10. Variations in the Number of Eyes in Early Ohio, 1903 



No. of' eyes 
Frequencies 


7 8 9 
14 2 


10 
6 


11 
21 


12 
21 


13 

25 


14 

36 


15 

37 


16 
17 


17 
12 


18 
15 


19 20 
7 11 


21 

2 


22 
2 



6. Type of soil. — It is well known that the physical type of 
soil best 'suited for the growth of potatoes is a light sandy loam. 
These investigations from 1902-1904 were carried on in the black 
heavy loam characteristic of the corn belt of the central west and 
in 1905-1906 on a light sandy loam in Connecticut. No stock 
from the same strain was available for test, and as the influence 
due to climate and soil is unknown, we have scarcely a warrant 
to make comparisons. Published analyses, however, show a 
higher percent of dry matter in potatoes grown on the light sandy 
loam, and the quality of tested tubers from the same variety 



432 Bulletin No. 127. [August, 

m 

though not from the same stock, was perceptibly better on this 
type of soil. In a test of Early Ohio potatoes on the heavy loam 
soil, planting to a depth of five inches gave potatoes of a much 
better quality than potatoes which were planted to a depth of 
three inches. The same was true of Carman No. 3 planted on a 
light sandy soil, but potatoes planted three inches deep and ridged 
at the last cultivation were of poorer quality than those unridged. 
This coincides with Gilmore's extensive work where he found that 
about five inches depth showed a more uniform temperature dur- 
ing the season than did other depths. 

7. Season and climate. — Season and climate are undoubtedly 
factors in determining quality, though whether they have an in- 
fluence beyond that of giving the plant greater or less chance for 
producing healthy, mature tubers, it is impossible to say. As po- 
tatoes are known to have a very great range of altitude and lati- 
tude when conditions of soil are right, we are inclined to think 
that the latter is the only influence. 

8. Influence of fertilizers. — The influence of fertilizers seems 
to be primarily if not solely due to their aid in producing a normal 
development of tubers. That is, the fertilizer applied must correct 
abnormality by furnishing an element of fertility which is lacking 
in the soil. An application of ordinary quantities of an essential 
element which is already present in the soil in amounts necessary 
to a normally fertile soil, probably has no marked effect either 
upon the crop or its quality. 

Some writers have maintained that the use of potassium sul- 
fate gives potatoes of better quality than are produced with the 
use of potassium chlorid, but this conclusion is opposed by other 
experiments. There is probably no ill effect from the use of or- 
dinary amounts (100 to 500 lb.*) of potassium chlorid, even if 
excessive use of chlorids is detrimental. 

The following table shows the general effect of fertilizers upon 
quality. In an experiment planned primarily an soil fertility, 
sodium nitrate was sown at the rate of 250 lb. to the -acre over 
the whole plot and potassium and phosphorus supplied as shown 
in the table. The numbers here shown are the estimates of qual- 
ity of all of the tubers produced by all of the plants of one row 
running across all the plots. The variety used was Green Moun- 
tain. The land was very poor in fertility although in excellent 

•Potatoes of excellent quality have been tested, which were grown with this rate of potas 
sium chlorid but no comparisons were made with like amounts of potassium sulfate. 



jgoS.] 



Improvement of the Potato. 



433 



physical condition for growing potatoes. It was known, however, 
that it was not nearly so deficient in phosphorus as in potassium. 
As is seen, the quality grew markedly better where the potassium 
chlorid was supplied at the rate of 300 lb. per acre, but apparently 
very little difference was made by doubling the applications of 
phosphorus. 

Table ii. Influence of Fertilizers on Quality 



Plot 


Fertilizers 
applied 
per acre. 


No. 
tubers 

pro- 
duced. 


No. of tubers of each of these qualities. 


No. 


Good. 


Fair. 


Me- 
dium. 


Poor. 


Very 
poor. 


1 

2 

3 
4 

5 


Nothing. 

Potassium 
chlorid 
150 lbs.. 

Bone meal 
200 lbs. 

Potassium 
chlorid 
300 lbs.. 

Bone meal 
100 lbs. 

Potassium 
chlorid 
300 lbs.. 

Bone meal 
200 lbs. 

Potassium 
chlorid 
300 lbs., 

Bone meal 
400 lbs. 


81 
125 

121 

148 

135 




1 

1 
3 
3 


5 
10 

12 

14 

19 


17 
33 

42 

56 

56 


25 
56 

40 

45 

37 


34 

25 

26 
30 
20 



The explanation of this fact is apparent, I think, in the next 
table, which shows the number of tubers produced of different 
classes of 30 grams each. There was simply a more nearly normal 
development of the tubers in the last three plots, due to the avail- 
ability of more potassium. 



434 



BULLOIN No. 127. 



[August, 



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igoS.] 



Improvement of the Potato. 



435 



9. Degree of maturity. — In 1902, a number of potatoes of 
Rural New Yorker No. 2 variety, of different degrees of maturity, 
were analyzed. The determinations showed that the greater part 
of the total nitrogen is developed early in the growth of the tuber, 
while the starch is stored up later. A microscopical examination 
showed that the starch grains in the cells of the immature tubers 
are small in size and few in number. Starch grains in the cortical 
and outer medullary layers of mature tubers averaged about 75 
)u,. and were found as large as 105 m. ; while in immature tubers 
of less than an ounce in weight, the starch grains averaged only 
25 /^- , ^ .■',::. 

Table 13. Composition of Tubers of Different Degrees of Maturity 
Averages of a Number of Tubers 



*Degree of maturity. 


Dry matter, 
percent. 


Protein fresh 
basis, percent. 


Protein dry 
basis, percent. 


Very immature 

Immature 


8.01 
11.15 
16.70 
21.20 


1.22 
1.66 
2.15 
1.94 


15.23 
14.93 


Fairly mature 

Mature 


12.85 
9.16 







These tubers, — as might be expected from their composition, 
— increased in desirability for table use with maturity to such an 
extent that we may conclude that all immature potatoes should be 
rejected for cooking. 

This fact seems a reasonable explanation of the influence that 
certain other minor factors seem to have on quality, such as dis- 
tance apart and time of planting, depth and frequency of cultiva- 
tion, etc. In fact any and all of the conditions of environment 
that lead to the normal development of healthy, mature potatoes 
may be considered as contributing toward their table equality. 

As a result of these tests, we are led to the following conclu- 
sions regarding quality : 

I. Quality depends upon the following factors: a. Homo- 
geneous anatomical structure. In general, quality increases with 
the thickness of the cortical layer, and decreases as the number 
of eyes increases. A variety shape which gives a chance for a 
large ratio of cortical to inner medullary layer, is an advantage 
b. Dry matter content. This must be such that the cooked starch 
fills the cells to their bursting point. The lower limit is roughly 
estimated at 18 percent, c. Maturity. This is affected by all 

*Weitfhts of the different classes were approximately 50 g-., W g., 150 g. and 250 g-. 



436 Bulletin No. 127. * [August, 

factors of soil physics, soil fertility, cultivation and climate dur- 
ing the growing period. 

2. Under like conditions of environment, variations in table 
quality are shown as varietal characteristics due to heritable dif- 
ferences in shape, composition and physical structure. 

3. These heritable differences can probably be used as a basis 
for improvement in quality when originating new varieties. 

4. There are also variations in quality within a variety which 
are in large measure due to immediate external conditions. These 
fluctuations obscure the heritable variations upon which improve- 
ment depends. / 

5. The question as to whether partial fluctuations of these char- 
acters obey the same laws as individual fluctuations, and whether 
temporary improvement can be made through their selection is yet 
undecided. The truth of Johannsen's theory of the fluctuations of 
"pure lines" would answer this in the negative. 



I908.] 



Improvement of the Potato. 



437 



lo. VARIATION OF THE POTATO IN CHEMICAL COM- 
POSITION AS A BASIS FOR ITS IMPROVEMENT 

In 1902 work was started to determine whether there were 
sufficient variations of the proteid content within a variety of 
potatoes to warrant selection of individuals high in protein to 
endeavor to raise the average protein content of the variety. It 
was expected later that this work would throw some light upon Jo- 
hannsen's theory that in "pure lines" (self- fertilized lines), fluc- 
tuations regress completely to the mode of the pure line and not 
toward the mode of the general population. If this is true, abso- 
lutely no change could be made by selecting partial fluctuations. 
Johannsen's work was not reported until after the results of these 
two seasons had been obtained, but the data are here reported just 
as it was collected in 1904. 

About two bushels of potatoes of uniform type were selected 
from a carload of the variety Rural New Yorker No. 2. They 
were all grown in the same county in Wisconsin, but it could not 
be definitely stated that they were all grown in the same field or 
upon the same type of soil although the latter is likely. They were 
of good appearance and average 223 g. in weight. The smallest 
potato used weighed 141 g. and the largest 328 g. Over one-half 
of the tubers varied less than 30 g. from the average. The table 
quality was good for the time of the year, it being the month of 
May. ' 

Total nitrogen, dry matter and specific gravity determinations 
were made on one hundred seventy-nine tubers. The total nitrogen 
was determined by the regular Kjeldahl method; dry matter by 
drying to constant weight at I04°C in a glycerol oven in a current 
of hydrogen; and the specific gravity by the weight in air and the 
weight in distilled water at 20°C. Considerable variation was 
shown in the content of the dry matter and the average was found 
to be very low for potatoes of such good quality. This condensed 
table shows the extent of the variation, the extremes being 15.18 
percent and 28.27 percent. 



Table 14. Variation in Dry Matter in Rural New Yorker No. 2, Crop 

OF 1901 



Dry matter, percent. 

Frequency 

Dry matter, percent. 
Frequency 



15-16 


16-17 


17-18 


18-^9 


19-20 


20-21 


1 


7 


9 


17 


32 


39 


22-23 


23-24 


24-25 


25-26 


26-27 


27-28 


18 


11 


3 


5 


2 






21-22 

34 

28-29 

1 



438 



Bulletin No. 127. 



August, 



For calculating total nitrogenous matter we have used Frisby's 
and Bryant's (38) factor of 5.5 times the total nitrogen. The 
proteid nitrogen is probably about 55 percent to 60 percent of these 
numbers, but as it is still questionable as to what dietetic value 
should be placed upon non-proteid forms of nitrogen, they were 
not determined. The total nitrogenous matters are reported, cal- 
culated to the water free material. The extremes are 6.63 percent 
and 15.69 percent. 

Table 15. Variation in Total Nitrogenous Matter in Rural New Yorker 
No. 2, Crop of 1901. Dry basis 



Nitrogenous 
matter in 
percent. . 


6-7 


7-8 


8-9 


9-10 


10-11 


11-12 


12-13 


13-14 


14-15 


15-16 


Frequency. 


3 


4 


7 


18 


33 


43 


30 


23 


12 


6 



This table shows a surprising variability in composition in 
potatoes of the same variety. The extremely high percentage of 
nitrogenous constituents shows that there may be a basis for the 
origination of a variety equal in proteid content to a number of 
the varieties of dent maize now grown, could a variety with the 
composition of the highest fluctuations be perpetuated. Certainly, 
in this variety at least, the tubers do not deserve to be ranked as 
solely a starch food. 

A number of points were observed in looking over the complete 
data which are too bulky to publish. 

1. The nitrogen content does not vary directly with the num- 
ber of eyes. Therefore, in potatoes of the same size, many stems 
have no greater amount of nitrogen to draw upon in sprouting, 
than have a few. 

2. Variations in nitrogen content are not correlated with par- 
ticular shapes, 

3. Smaller, younger tubers are richer in nitrogen; that is, 
there is stored early in the formation of the tuber a relatively larger 
proportion of the total nitrogen than of starch. 

4. The error in determining starch from specific gravity tables 
is much greater than is generally supposed. For example, tuber 
No. 82 contains 14.32 percent nitrogenous matter, specific gravity 
1.090; while tuber No. 69 contains 7.39 percent nitrogenous mat- 
ter, specific gravity 1.091. 



J9o8.] 



Improvement of the Potato. 



+39 



Selections for Planting, 1902 

To endeavor to determine whether these fluctuations in a chem- 
ical constituent are transmitted by tuber propagation, two plots 
were planted, one of high nitrogen selections and one of low nitro- 
gen. This gives a check upon the seasonal and soil variations. The 
selections were made upon the fresh substance, because this is their 
market condition, and because the dry matter determinations were 
not finished soon enough to make selections on the water free basis 
practicable. 

As may be seen in the table, potatoes were chosen with as 
nearly as possible the same average weight. The low protem se- 
lections, however, averaged about i8g. heavier per tuber. 

The average nitrogenous matter in the high portein plot was 
2.95 percent of the fresh substance and 14.07 percent calculated to 
the water free substance. The following data were taken on each 
tuber. The long, medium and short diameters give a fair indica- 
tion of the shapes of the tubers : 

Table i6. High Protein Selections in 1902 



No. 


Wt. 

per 

cent. 


Long- 
diam. 


Me- 
dium 
diam. 


Short 
diam . 


No 
eyes 


Specific 
gravity. 


Dry 
matter 
percent. 


Nitroge- 
nous 
matter, 

fr. b. 
percent. 


Nitrog-e- 
nous 

matter. 

dry b., 
percent. 


44 

63 

68 

80 

82 

99 

104 

107 

111 

113 

117 

129 

137 

147 

166 


246 
279 
178 
198 
232 
182 
294 
228 
155 
221 
141 
199 
177 
166 
190 


98 

115 

90 

88 

100 

95 

122 

115 

75 

98 

90 

91 

85 

90 

90 


75 
68 
65 
70 
68 
60 
70 
62 
62 
65 
57 
66 
63 
64 
65 


55 
60 

53 
55 
52 
55 
58 
52 
55 
58 
46 
54 
48 
50 
51 


10 
14 
11 

9 
12 
16 
17 
18 

7 

19 
13 
12 
10 
10 
11 


1.095 
1.082 
1.090 
1.097 
1.090 
1.088 
1.091 
1.096 
1.095 
1.088 
1.100 
1.087 
1.096 
1.088 
1.098 


22.09 
19.49 
21.02 
20.74 
20.62 
22.21 
21.21 
21.41 
22.41 
19.19 
23.31 
19.75 
20.98 
20 45 
20.84 


2.93 
3.05 
2.95 
2.99 
2.95 
2.95 
2.87 
2.90 
2.90 
2.91 
3.09 
2.84 
2.90 
3.12 
2.95 


13.28 
15.69 
14.03 
14.44 
13.29 
13.29 
13.54 
13.53 
12.94 
15.16 
13.25 
14.41 
13.79 
15.30 
14.13 


Aver. 


205.7 








12.6 


1.092 


21.05 


2.95 


14.07 



Each potato was quartered and each quarter planted in a hill. 
The hills were four by two feet apart. The planting could not be 
done on account of press of other work until June tenth. 

In exactly the same manner, end to end with these selections, 
were planted the following low protein selections, which averaged 
1.78 percent nitrogenous matter in the fresh substance, and 8.75 
percent calculated to water free basis. 



440 



Bulletin No. 127. 



[August, 




Fig. 10. Potato Fruit. Natural size. 



The plants in the two plots were up about the same time, but 
owing to the wet season and late planting- on undrained land, were 
not vigorous. They were cultivated three times and sprayed twice 
with Paris green. Tip burn and Paris green injury combined to 
kill the plants very early. All plants on the two plots died at prac- 
tically the same time. 

Each potato planted produced from six to twenty tubers, but 
these were quite small, few being of marketable size. The tubers 
from the low protein plot were somewhat larger than those from 
the high protein plot. 



JQOS.] 



Improvement of the Potato. 



441 



Composite samples from the progeny of each tuber were made, 
and total nitrogen and moisture determined, as shown in the fol- 
lowing tables : 







Table 17. 


Low 


Protein Selections in 1902 




No. 


wt.gr. 


Long- 
diam. 


Me- 
dium 
diam. 


Short 
diam. 


No. 
Eyes. 


Specific 
Gravity. 


Dry 
Matter, 
percent. 


Protein 

fr. b. 
percent. 


Protein 

dry b. 

percent. 


3 


168 


86 


61 


49 


14 


1.099 


22.48 


1.91 


8.50 


6 


234 


113 


65 


52 


19 


1.092 


20.04 


1.93 


9.64 


23 


256 


107 


68 


53 


16 


1.087 


18.13 


1.64 


9.03 


51 


248 


104 


61 


57 


22 


1.091 


20.17 


1.79 


8.86 


59 


244 


101 


71 


52 


11 


1.098 


24.37 


1.65 


6.77 


65 


220 


105 


70 


55 


20 


1.102 


26.06 


1.72 


6 63 


69 


229 


105 


65 


55 


15 


1.091 


23.50 


1.73 


7.39- 


85 


199 


105 


74 


53 


12 


1.081 


16.35 


1.81 


11.11 


102 


243 


100 


71 


56 


13 


1.084 


17.54 


1.87 


10 66 


123 


221 


99 


66 


53 


15 


1.096 


21.45 


1.56 


7.28 


140 


198 


110 


63 


46 


17 


1.103 


23.15 


1.64 


7.08 


158 


229 


104 


70 


56 


17 


1.089 


19.10 


1.70 


8.91 


168 


170 


91 


62 


47 


10 


1.089 


19.86 


1.93 


9.72 


173 


272 


99 


73 


60 


14 


1.083 


19.73 


1.94 


9.83 


179 


218 


95 


67 


58 


10 


1.089 


19.65 


1.93 


9.81 


Aver. 


223 








14.9 


1.092 


22.10 


1.78 


8.75 



Table 18. High Protein Plot (Crop of 1902) 
(Weights, extremes 5 g. and 150 g., average 38 g.) 



Row 


From 


Dry matter 


Nitrogenous 


Nitrogenous 


No. 


potato No. 


percent. 


matter, fr. b. 


matter, dry b. 


1 


44 


13.55 


2.48 


18.48 


2 


63 


13.56 


2.51 


18.46 


3 


68 


10.50 


1.24 


11.83 


4 


80 


11.50 


1.39 


12.11 


*5 


82 


5.43 


1.04 


19.04 


*6 


99 


6.33 


1.18 


18.59 


7 


104 


14.54 


2.17 


14.96 


8 


107 


10.75 


1.28 


11.96 


9 


111 


8.00 


1.58 


19.81 


*10 


113 


7.25 


1.65 


22.81 


*11 


117 


7.00 


1.66 


23.74 


12 


129 


14.57 


1.79 


12.29 


13 


137 


13.92 


2.00 


14.35 


14 


147 


13.00 


2.25 


17.33 


15 


166 


14.83 


2.26 


15.26 


General average 


10.98 


1.765 


16.73 


Average after rejection 


13.07 


1.937 


14.70 



*Very small, rejected. 



442 



Bulletin No. 127. , 

Table 19. Low Protein Plot (Crop of 1902) 
(Weights, extremes 10 g. and 180 g., average 68 g.) 



[August, 



Row 


From 


Drv matter 


Nitrogenous 


Nitrogenous 


No. 


potato No. 


percent. 


matter, fr. b. 


matter, dry b. 


1 


3 


21.20 


1.94 


9.16 


2 


6 


16.42 


2.32 


14.16 


3 


23 


16.33 


2.10 


12.86 


*4 


51 


7.50 


1.25 


16.68 


5 


59 


11.15 


1.66 


14.93 


*6 


65 


8.26 


1.24 


15.02 


7 


69 


15.42 


2.31 


14.96 


*8 


85 


8.28 


1.16 


14.00 


9 


102 


15.33 


2.18 


14.27 


10 


123 


16.02 


1.92 


12.00 


11 


140 


14.55 


1.49 


10.20 


12 


158 


14.50 


2.02 


13.95 


*13 


168 


12.50 


1.12 


8.94 


14 


173 


17.23 


2.23 


12.95 


15 


179 


16.16 


2.06 


12.75 


General average 


14.056 


1.80 


13.12 


Average after rejection 


15.56 


1.945 


12.59 



*Very small, rejected. 

The general averages here, after rejecting the results from such 
hills as were far below marketable size indicate that there is 110 
definite response to selection for high or low protein. It is true 
that the average of nitrogenous matter when calculated to the 
water free basis is 2. 11 percent higher in the crop from the high 
nitrogen selections than in the crop from the low nitrogen selec- 
tions. This, however, is wholly due to the difference in the aver- 
age contents of dry matter, for the nitrogenous matter when cal- 
culated to the fresh substance, are practically the same. 

There is an indication that the low protein potatoes are quicker 
to mature, for in the same growing period they had elaborated 
about twice as much fresh material, which contained 2.5 percent 
more dry matter than the high protein potatoes. 

The poor development of the potatoes this season necessitated 
a return to other seed for the continuation of the experiment. This 
reduces the value the results of the second migiit have, as it was 
the intention to continue selecting from the same stock, with the 
hope of testing a possible cumulative effect of selection. 



igoS.] 



Improvement of the Potato. 



443 



Selections for Planting, 1903 

The experiment was continued in 1903, with the variety Early 
Ohio, which was considered to give better yields on Illinois soil. 
Unfortunately, the seed tubers which w^ere obtained had been grown 
in southern Illinois on soil of an entirely different type from that 
upon w^hich they were to be planted in the experiment, and there is 
no means of knowing whether the stock was adapted to the latter 
type. 

These potatoes were of different type from those used in 1902. 
the Early Ohio being oblong-cylindrical. The average weight was 
smaller and the cooking quality poorer than those of the previous 
year. They were slightly infected with scab, but were fairly typ- 
ical of the variety. 

Two hundred nineteen individual tubers were analyzed in the 
same manner as those of the year before, with the result that fully 
as great variation in individuals was found in this variety. 

Comparing the two varieties. used (1902 and 1903), which of 
course is not strictly fair, owing to their being the product of dif- 
ferent soils and seasons, it is seen that the higher average dry mat- 
ter is shown in the round-flat variety, which is in accord with 
Fischer's theory. 

The dry matter fluctuations were from 10.55 percent to 30.96 
percent, with an average of 16.15 percent and a mode between 
16.0 percent and 17.0 percent. 



Table 20. Variations in Dry Matter. (Crop of 1902, Early Ohio) 



Dry matter, per- 
cent 



Frequencies. . . . 



10-11 
4 



11-12 

5 



12-13 

7 



13-14 
20 



14-15 
19 



15-16 
44 



16-1'; 

54 



17-18 

27 



18-19 

24 



19-20 
13 



20-21 

3 



The average nitrogenous matters, calculated to fresh basis is 

2.43 percent, and calculated to water free basis is 15.21 percent. 

The variations in total nitrogenous matter are shown in the fol- 
lowing table : 



444 



Bulletin No. 127. 



[August, 



Table 21. Variations in Total Nitrogenous Matter. 

Ohio. Dry Basis) 



(Crop of 1902, Early 



Nitrogenous 
matter, percent 


7-8 


8-9 


9-10 


10-11 


11-12 


12-13 


13-14 14-15 


15-16 


i 
I6-I7I17-I8 


Frequencies. . . . 


1 


1 





1 


7 


14 


39 


40 


46 


27 


11 


Nitrogenous 
matter, percent 


18-19 


19-20 


20-21 


21-22 


22-23 


23-24 


24-25 25-26 


26-27 


27-28 




Frequencies 


12 


8 


2 














1 





1 





The mode of nitrogenous matter is here between 15 percent 
and 16 percent. This is an amount of nitrogenous matter not to 
be despised. If the nitrogenous matter could be raised in the same 
proportion, when by cuUivation under better" conditions, a higher 
dry matter is obtained, there would be a food containing at least 
as much actual proteid nitrogen as many varieties of maize. It is 
highly probable that the two extreme high variations should be dis- 
regarded as errors, although potato No. 13 with a content of nitrog- 
enous matter of 27.46 percent, weighed only ,87 grams, which 
might account for rather high nitrogen content. The other tubers 
varied in weight from 150 to 300 grams. 

Twenty tubers were selected for the high protein plot and fif- 
teen for the low protein plot, selecting on the fresh basis, as before. 
The analyses of the individuals selected for planting are shown in 
Tables 22 and 23. 

Table 22. High Protein Selections. 1903 



Planted in 


Wt. Nit. matter 


Dry matter, 


Nit. matter, 


Sp. gr. 


row No. 


fresh basis. 


percent. 


dry basis. 


1 


2.78 


14.28 


19.42 


1.063 


2 


3.12 


15.53 


20.01 


1.058 


3 


2.93 


10.66 


27.46 


1.092 


4 


3.03 


15.10 


20.04 


1.060 


5 


2.78 


14.93 


18.60 


1.059 


6 


2.78 


15.35 


18.10 


1.061 


7 


2.80 


10.74 


25.91 


1.062 


8 


2.92 


16.74 


17.42 


1.059 


9 


2.90 


18.85 


15.36 


1.064 


10 


2.80 


15.66 


17.85 


1.056 


11 


2.79 


17.60 


15.81 


1.062 


12 


2.77 


15.34 


18.06 


1.062 


13 


2.83 


18.96 


14.91 


1.069 


14 


2.81 


16.99 


16.53 


1.069 


IS 


2.86 


17.99 


16.39 


1.067 


16 


2.93 


19.62 


14.93 


1.074 


17 


2.83 


17.36 


16.31 


1.063 


18 


2.85 


18.94 


15.04 


1.066 


19 


2.77 


16.18 


17.10 


1.066 


20 


2.77 


17.49 


,15.85 


1.060 


General av. 


2.85 


16.215 


18.055 


1.064 



jgoS.] 



Improvement of the Potato. 
Table 23. Low Protein Selections. 1903 



445 



Planted in 


Wt.Nit. matter 


Dry matter 


Nit. matter 


Sp. gr. 


row. No. 


fresh basis. 


percent. 


dry basis. 


1 


1.97 


13.37 


14.71 


1.054 


2 


2.01 


11.30 


17.74 


1.037 


3 


1.88 


13.08 


14.40 


1.038 


4 


2.02 


14.03 


14.32 


1.026 


5 


1.46 


10.77 


13.56 


1.040 


. 6 


1.68 


11.17 


15.01 


1.034 


7 


1.96 


12.62 


15.55 


1.044 


8 


1.72 


12.22 


14.09 


1.045 


9 


1.80 


11.86 


15.16 


1.045 


10 


1.97 


13.26 


14.81 


1.050 


11 


1.60 


12.93 


12.39 


1.045 


12 


1.38 


19.30 


7.14 


1.034 


13 


1.98 


16.81 


11.78 


1.059 


14 


1.68 


19.99 


8.39 


1.032 


15 


1.65 


14.30 


11.53 


1.043 


General av. 


1.78 


13.80 


13.37 


1.0417 



There was a noticeable difference this year in the contents of 
dry matter of the two selections. The tubers planted in the high 
protein plot average 2.42 percent higher than those planted in the 
low protein plot. This reduces the average difference in content of 
nitrogenous matter between the tubers of the two classes, but 
there is still a difference of 4.69 percent, when calculated to the 
water free basis. This matter is of interest because it definitely 
shows that in mature tubers, a high percentage of nitrogenous mat- 
ter is not correlated with a low dry matter content. This is addi- 
tional evidence that potatoes of good quality, other things being 
equal, may be high in nitrogen. The average weight of the selec- 
tions for the low protein plot was nine grams higher than those for 
the high protein plot. 

The tubers were quartered and were planted in the same man- 
ner as in the year before, but on slightly better soil. The planting 
was done May 18, 1903, and the potatoes were up June second. 
Every cutting grew, but the growth was not luxuriant. It is 
thought that the seed may have been injured by the formalin treat- 
ment for scab. The plots were given ordinary farm cultivation, 
and were sprayed three times with Paris green and once with Bor- 
deaux mixture. 

The plants in both plots succumbed to tip burn and Paris green 
injury about the same time. The crop was larger than that of the 
year before, but not nearly all of the tubers were of marketable 
size. The potatoes were of different degrees of immaturity, but were 
sufficiently mature to make a fair comparison. Seventy-five per- 
cent by weight of the crop from the high protein plot averaged 75 



446 



Bulletin No. 127. 



[August, 



grams in weight, while seventy-five percent by weight of the crop 
from the low protein plot averaged 70 grams in weight. The 
analyses of composite samples are given in the following tables : 

Table 24. High Protein Plot. (Crop of 1903) 



Row No. 


Dr>' matter, 
percent. 


Nit. matter, 
fresh basis. 


Nit. matter, 
dry basis. 


1 


17.01 


1.88 


11.08 


2 


18.04 


1.72 


9.57 


3 


19.32 


1.98 


10.24 


4 


17.65 


2.04 


11.57 


5 


15.50 


1.88 


12.13 


6 


17.58 


2.00 


11.35 


7 


17.19 


1.90 


11.04 


8 


17.75 


2.32 


13.08 


9 


13.48 


1.97 


14.63 


10 


13.68 


1.62 


11.84 


11 


15.44 


1.50 


9.75 


12 


16.23 


1.62 


9.98 


13 


14.53 


1.44 


9.95 


14 


16.11 


1.87 


11.62 


15 


15 02 


1.75 


11.67 


16 


15.84 


1.71 


10.78 


17 


14.02 


1.51 


10.82 


18 


15.98 


1.39 


8.71 


19 


14.31 


1.28 


8.96 


20 


13.83 


1.27 


9:16 


Gen. ave. . . 


15.93 


1.73 


10.90 





Table 25. Low Protein Plot. (Crop of 


1903.) 






Row No. 


Dry matter, 


Nit. matter. 


Nit. matter, 






percent. 


fresh basis. 


dry basis. 




1 


14.80 


1.23 


8.32 




2 


14.11 


1.20 


8.47 




3 


15.93 


1.44 


9.06 




4 


15.72 


1.30 


8.31 




5 


15.61 


1.36 


8.76 




6 


14.68 


1.58 


10.76 




7 


13.87 


1.28 


9.27 




8 


16.41 


136 


8.26 




9 


15.94 


1.46 


9.15 




10 


14.92 


1.37 


9.23 




11 


14.98 


1.30 


8.69 




12 


14.38 


1.76 


12.28 




13 


13.91 


1.31 


9.42 




14 


15.28 


1.52 


9.96 




IS 


16.21 


15.1 


9.32 




Gen. ave. . . 


15.12 


1.40 


9.29 





igoS.] Improvement of the Potato. 447 

No very definite conclusions can be drawn from this one sea- 
son's work, yet in comparing a possible inheritance of variations, 
the difference of .81 percent in dry matter is noteworthy. It should 
be remembered that the low protein potatoes were larger and from 
them should ha\-e ordinarily been expected the higher dry matter. 
The difference in total nitrogenous matter, in favor of the high 
protein plot was 0.33 percent upon the fresh sample and 1.61 per- 
cent upon the dried sample. The regression of each plot toward 
the same type in percentages of dry matter and nitrogenous mate- 
rial is great but no more than would have been expected from seed 
propagated selections. 

Note. — This experiment is being continued on a somewhat dif- 
ferent plan. A variety of potatoes has been produced, coming from 
a single tuber of a seedling of four years ago. With these tubers 
two plots are being carried on, one for high and one for low nitro- 
gen. It is expected by thus having a check upon the effects of soil, 
and having to deal with an accurately estimated character, to be 
able definitely to demonstrate whether there is inheritance of asex- 
ual fluctuations. 

General Statements 

The improvement of our present varieties of potatoes in yield- 
ing power, and the enhancing of particularly valuable characters 
through breeding and selection have been shown in the foregoing 
pages to be broad and many sided questions. They are beset with 
difficulties such as are attendant on the improvement of no other 
important field crop. But if the questions are dif^cult, some cf them 
are far reaching in their bearing and the subject seems alike wor- 
thy the attention of the biologist seeking experimental evidence 
concerning the meaning of sex and the inheritance of fluctuating 
characters ; and the practical breeder whose relative success in the 
production of new varieties is measured by dollars and cents. 

The use of other tuber bearing species of Solanum as a starting 
point for new varieties has not yet produced anything of value. 
Hope is still entertained that S. Commersonn crossed, or hybrid- 
ized, with S. tuberosum will finally produce something that is dis- 
ease resistant and satisfactory in other respects. The present evi- 
dence, however, seems to point towards some correlation of quality 
with susceptibility to disease, so that definite knowledge of the 
physiological meaning of fungus resistance is most probably the 
kev to the door we must enter. 



448 Bulletin No. 127. [August, 

The fairly extensive recorded history of S. tuberosum for three 
hundred years is interesting to the student of changes under do- 
mestication, in that the changes which have taken place in the plant 
have been almost entirely in the selected part, the tuber. Even the 
change in the tubers seems to be largely a matter of lesser numbers 
and larger size per plant. The minor distinctions that have sepa- 
rated modern varieties have been in the main those of shape and 
color. Slight differences, provided the variety is a fairly high 
yielder, have been the cause of a large number of names, but in the 
United States, at least, the productions of scientific breeders com- 
paratively few in number, furnish practically the entire crop of the 
country. 

Methods of hybridizing the potato are comparatively simple, 
but the variation of the varieties in their ability to furnish viable 
pollen has been a source of disappointment with a great many 
varieties possessiftg other particularly good characters. A problem 
here is to find means of stimulating the production of pollen in 
these varieties. This matter is also of special theoretical interest 
in its bearing on the production of sex. 

The method of propagating the potato has seriously increased 
the number of errors in making comparative field tests during the 
establishment of varieties. The fact that the seedlings must be 
grown several years in the comparison test before making definite 
selections, makes care in this respect still more important. The dis- 
covery of characters in the young plant which are correlated with 
characters in the tuber would be of great advantage in shortening 
the time of their comparison before final rejection of the unfit. 
Some work has already been done in this direction. 

Possible methods of improvement are three : 

1. The crossing of desirable plants and raising of many seed- 
lings under controlled conditions. 

2. Selections of the most desirable fluctuations among the plants 
and tubers of a variety. 

3. Selection of discontinuous variations, and a study of ways 
of causing them, a possible example being the so-called graft-hybrid. 

That advance is possible by the first method is admitted from 
the results of its use by the best breeders. More data as to the best 
details for work in use of this method, however, are very desirable. 
Whether results can be obtained by the second method has not been 
definitely proved. The data here shown which do point to the af- - 
firmative, are not conclusive. Isolated cases of improvement might 
reasonably be explained as due to mutations. 



igo8.] Improvement of the Potato. 449 

The hypothesis of degeneration seems to have Httle ground 
either in theory or in practice. Disease control is here of para- 
mount importance. 

Table quality, according to the American standard, depends pri- 
marily upon homogenous structure of the tuber, when mature tu- 
bers of a fair percentage dry matter are compared. This condition 
is to a large extent a varietal character and as such is probably 
capable of improvement. That this can be done by selection of 
tubers within a variety has not yet been definitely determined, but 
is improbable. 

Tubers with a total content of nitrogenous matter beyond the 
average for maize (calculated to dry basis) have been found. It 
has been shown that a high nitrogen content, at least within the 
limit found, is not through any law of composition, opposed to our 
conception of quality. 

That varieties can be produced with a much higher food value 
because of their higher nitrogen content, by selection of seedlings 
from their chemical analysis is not to be doubted. 



450 Bulletin No. 127. [Augtisi, 



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i^o8.] Improvement of the Potato. 451 

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igo8.] Improvement of the Potato. *53 

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454 Bulletin No. 127. ^ [August, 

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jgoS.] Improvement of the Potato. 4-55 

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203. 



456 Bulletin No. 127. [August, igo8.] 

109. WoLLNY, E., — Einfluss des Anwelkens der Saatknollen auf 
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111. WoLivNY, E., — Einfluss der Anwelkens der Saatknollen auf 
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112. W0LI.NY, E., — Einfluss des Ausbohrens der Seitenknospen an 
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113. WoLivNY, E., — Einfluss des Anwelkens der Saatknollen auf 
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114. Woi,i,NY, E., — Untersuchungen iiber die Beeinflussung des 
Productionsvermogens der Kartoffelpflanze durch Beniitzung 
gekeimter Saatknollen. Forsch. Agr. 19:443-462. 1896. 



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